WO2015166303A1

WO2015166303A1 - Denying random access attempts under excessive received power conditions

Info

Publication number: WO2015166303A1
Application number: PCT/IB2014/061121
Authority: WO
Inventors: Babak Alamshahi; Tomas BRÄNNLUND; Patrik Karlsson
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-04-30
Filing date: 2014-04-30
Publication date: 2015-11-05

Abstract

Systems and methods for mitigating uplink interference due to uplink random access transmissions are disclosed. In one embodiment, a method of operation of a radio access node is provided. In one embodiment, the method of operation of the radio access node includes detecting a random access attempt made by a wireless device, determining whether one or more conditions indicative of an excessive received power condition at the radio access node are satisfied, and sending a denial of the random access attempt to the wireless device if the one or more conditions are satisfied. In this manner, an increase in uplink interference due to a subsequent random access transmission (e.g., transmission of a random access message) is avoided.

Description

DENYING RANDOM ACCESS ATTEMPTS UNDER EXCESSIVE RECEIVED

POWER CONDITIONS

Field of the Disclosure

[0001] The present disclosure relates to mitigating uplink interference in a cellular communications network and more specifically relates to mitigating uplink interference via uplink overload control.

Background

[0002] The Universal Terrestrial Radio Access Network (UTRAN) is a cellular radio access network based on Wideband Code Division Multiple Access

(WCDMA) technology and is standardized by the Third Generation Partnership Project (3GPP). The UTRAN is also referred to as a WCDMA Radio Access Network (WRAN). As in all types of cellular Radio Access Networks (RANs), wireless devices access the WRAN via a random access procedure. In this random access procedure, a wireless device transmits a random access transmission that consists of: (a) one or several preambles (referred to as a Random Access Channel (RACH) preamble(s)) each having a length of 4096 chips and (b) a message having a length of 10 milliseconds (ms) or 20 ms. Each RACH preamble has a length of 4096 chips and consists of 256 repetitions of a signature having a length of 16 chips. There is a maximum of 16 available signatures. When transmitting the random access transmission, the wireless device starts the transmission of the RACH preamble by randomly choosing a signature to transmit in a first access slot and starts the random access transmission at an initial power. The wireless device then continues the transmission of the RACH preamble by randomly choosing signatures for successive access slots and ramping up the transmit power until a base station responds with an Acquisition Indicator Channel (AICH) Acknowledgement (ACK)/ Negative Acknowledgement (NACK) or until a predefined time-out period has passed.

[0003] Upon reception of the RACH preamble at the base station, the base station estimates a Signal-to-lnterference Ratio (SIR) for the received RACH preamble. The base station returns an AICH ACK to the wireless device in the downlink if the SIR is above a certain threshold, which is referred to herein as a preamble threshold. The preamble threshold is a system constant parameter with a default value of, e.g., 19 decibels (dB). A wireless device in a fading environment might have ramped up the transmission power level for the RACH preamble significantly before a RACH AICH was sent in response to the RACH preamble. When the RACH preamble is acknowledged, the wireless device starts transmission of the RACH message after some slot delay. The transmit power for the RACH message is based on the RACH preamble by adding an offset value to the transmit power to which the wireless device had ramped-up to during transmission of the RACH preamble. Consequently, a high RACH preamble SIR will cause high RACH message SIR and will contribute to increase Rise-over-Thermal (RoT) (i.e., increase uplink interference). Summary

[0004] Systems and methods for mitigating uplink interference due to uplink random access transmissions are disclosed. In one embodiment, a method of operation of a radio access node is provided. In one embodiment, the method of operation of the radio access node includes detecting a random access attempt made by a wireless device, determining whether one or more conditions indicative of an excessive received power condition at the radio access node are satisfied, and sending a denial of the random access attempt to the wireless device if the one or more conditions are satisfied. In this manner, an increase in uplink interference due to a subsequent random access transmission (e.g., transmission of a random access message) is avoided.

[0005] In one embodiment, the one or more conditions include a condition that a Signal-to-lnterference Ratio (SIR) for the random access attempt is greater than a predefined SIR threshold. In another embodiment, the one or more conditions include a condition that a Rise-over-Thermal (RoT) for a cell served by the radio access node for which the random access attempt is made is greater than a predefined RoT threshold. [0006] In one embodiment, detecting the random access attempt includes detecting a Random Access Channel (RACH) preamble. Further, in one embodiment, the one or more conditions include a condition that a SIR for the RACH preamble is greater than a predefined SIR threshold. In another embodiment, the one or more conditions include a condition that a RoT for a cell served by the radio access node for which the random access attempt is made is greater than a predefined RoT threshold.

[0007] In one embodiment, the method further includes determining whether one or more conditions for sending a denial of the random access attempt to the wireless device are satisfied. In this embodiment, sending the denial of the random access attempt to the wireless device includes sending the denial of the random access attempt to the wireless device if the one or more conditions indicative of the excessive received power condition are satisfied and the one or more conditions for sending the denial of the random access attempt to the wireless device are satisfied. In one embodiment, the one or more conditions for sending the denial of the random access attempt include a condition that a signature detected in the RACH preamble be one of a subset of possible signatures for which random access attempts are to be denied. In another embodiment, the one or more conditions for sending the denial of the random access attempt include a condition that a predefined percentage of random access attempts are to be denied when a cell load of the cell served by the radio access node for which the random access attempt is made is greater than a predefined threshold.

[0008] In one embodiment, sending the denial of the random access attempt to the wireless device includes sending an Acquisition Indicator Channel (AICH) Negative Acknowledgement (NACK) to the wireless device.

[0009] In one embodiment, the cellular communications network is a

Wideband Code Division Multiple Access (WCDMA) cellular communications network.

[0010] In another embodiment, a radio access node for a cellular

communications network is provided. In one embodiment, the radio access node includes a transceiver, a processor associated with the transceiver, and memory containing software instructions executable by the processor whereby the radio access node is operative to detect a random access attempt made by a wireless device, determine whether one or more conditions indicative of an excessive received power condition are satisfied, and send a denial of the random access attempt to the wireless device if the one or more conditions are satisfied.

[0011 ] In another embodiment, a radio access node is adapted to detect a random access attempt made by a wireless device, determine whether one or more conditions indicative of an excessive received power condition are satisfied, and send a denial of the random access attempt to the wireless device if the one or more conditions are satisfied.

[0012] Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the embodiments in association with the accompanying drawing figures.

Brief Description of the Drawing Figures

[0013] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0014] Figure 1 illustrates a cellular communications network according to one embodiment of the present disclosure;

[0015] Figure 2 is a flow chart that illustrates the operation of the base station of Figure 1 to provide uplink load control by denying a random access attempt of a wireless device when one or more excessive received power conditions are met according to one embodiment of the present disclosure;

[0016] Figure 3 illustrates the operation of the base station of Figure 1 to detect a Random Access Channel (RACH) preamble transmitted by a wireless device and respond with an Acquisition Indicator Channel (AICH) NACK upon determining that one or more excessive received power conditions are met according to one embodiment of the present disclosure; [0017] Figure 4 is a flow chart that illustrates the operation of the base station of Figure 1 to deny a random access attempt from a wireless device when a Signal-to-lnterference Ratio (SIR) for the received RACH preamble is greater than a predefined maximum SIR threshold according to one embodiment of the present disclosure;

[0018] Figure 5 is a flow chart that illustrates the operation of the base station of Figure 1 to deny a random access attempt from a wireless device when a Rise-over-Thermal (RoT) measurement associated with the received RACH preamble is greater than a predefined maximum RoT threshold according to another embodiment of the present disclosure;

[0019] Figure 6 is a flow chart that illustrates the operation of the base station of Figure 1 to deny a random access attempt from a wireless device when a SIR for the received RACH preamble is greater than a predefined maximum SIR threshold and a RoT measurement associated with the received RACH preamble is greater than a predefined maximum RoT threshold according to another embodiment of the present disclosure;

[0020] Figure 7 is a flow chart that illustrates the operation of the base station of Figure 1 to deny a random access attempt from a wireless device when a SIR for the received RACH preamble is greater than a predefined maximum SIR threshold and one or more additional predefined conditions for denying the random access attempt are met according to another embodiment of the present disclosure;

[0021] Figure 8 is a flow chart that illustrates the operation of the base station of Figure 1 to deny a random access attempt from a wireless device when a RoT measurement associated with the received RACH preamble is greater than a predefined maximum RoT threshold and one or more additional predefined conditions for denying the random access attempt are met according to another embodiment of the present disclosure;

[0022] Figure 9 is a block diagram of the base station of Figure 1 according to one embodiment of the present disclosure; and [0023] Figure 10 is a block diagram of the base station of Figure 1 according to another embodiment of the present disclosure.

Detailed Description

[0024] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

[0025] Systems and methods for mitigating uplink interference due to uplink random access transmissions are disclosed. In this regard, Figure 1 illustrates a cellular communications network 10 according to one embodiment of the present disclosure. In some embodiments, the cellular communications network 10 is a Wideband Code Division Multiple Access (WCDMA) cellular communications network as defined by the Third Generation Partnership Project (3GPP). More specifically, in some embodiments, a Radio Access Network (RAN) of the cellular communications network 10 is a WCDMA RAN (WRAN). As such, 3GPP WRAN terminology is sometimes used herein. However, the present disclosure is not limited to a WRAN. Rather, the embodiments disclosed herein may be utilized in any suitable type of cellular RAN.

[0026] As illustrated, the cellular communications network 10 includes a base station 12, which in 3GPP RAN is referred to as a Node B. Note that while many of the embodiments disclosed herein are described with respect to the base station 12, the embodiments disclosed herein are equally applicable to other types of radio access nodes. The base station 12 provides wireless, or radio, access to a number of wireless devices 14 (generally referred to herein collectively as wireless devices 14 and individually as wireless device 14) located within a cell 16, or coverage area, of the base station 12. [0027] The wireless devices 14 request a connection setup with the base station 12 using a random access procedure. In a conventional WRAN, a wireless device 14 transmits a random access transmission that consists of: (a) one or several preambles (referred to as a Random Access Channel (RACH) preamble(s)) each having a length of 4096 chips and (b) a message having a length of 10 milliseconds (ms) or 20 ms. Each RACH preamble has a length of 4096 chips and consists of 256 repetitions of a signature having a length of 16 chips. There is a maximum of 16 available signatures. For the random access transmission, the wireless device 14 transmits a series of randomly selected signatures while ramping up the transmit power from an initial transmit power until the base station 12 responds with an Acquisition Indicator Channel (AICH) Acknowledgement (ACK)/ Negative Acknowledgement (NACK) or until a predefined time-out period has passed.

[0028] At the base station 12, upon reception of the RACH preamble transmitted by the wireless device 14, the base station 12 estimates a Signal-to- Interference Ratio (SIR) for the received RACH preamble. The base station 12 returns an AICH ACK to the wireless device 14 in the downlink if the SIR is above a certain threshold, which is referred to herein as a preamble threshold, and there are sufficient hardware resources to decode the RACH message. The preamble threshold is a system constant parameter with a default value of, e.g., 19 decibels (dB). The base station 12 returns an AICH NACK to the wireless device 14 if the SIR is above the preamble threshold but there are insufficient hardware resources to decode the RACH message. If the wireless device 14 receives an AICH ACK from the base station 12, the wireless device 14 starts transmission of the RACH message after some slot delay. The transmit power for the RACH message is based on the RACH preamble by adding an offset value to the transmit power to which the wireless device 14 had ramped-up to during transmission of the RACH preamble.

[0029] One issue with the conventional random access procedure described above is that the transmission of the RACH message increases uplink interference particularly in scenarios where the SIR of the RACH preamble is high due to, for example, a fading environment. More specifically, the wireless device 14 attempting to transmit a RACH preamble determines an initial transmit power for the RACH preamble based on: (1 ) primary Common Pilot Channel (CPICH) transmit power, (2) measured CPICH received signal code power, (3) uplink interference level in the cell 16, and (4) a constant value, i.e., an offset to be added in the calculation of the initial transmit power for the RACH preamble. The CPICH transmit power, the uplink interference, and the constant value are broadcast from the base station 12 to the wireless devices 14 in a broadcast channel. The wireless device 14 measures the CPICH received signal code power, which defines a pathloss for the CPICH signal from the base station 12 to the wireless device 14. In particular, the pathloss is the difference between the CPICH transmission power and the measured CPICH received signal code power. Depending on a sensitivity of a receiver of the wireless device 14, an accuracy of the calculated pathloss will vary.

[0030] Another factor that impacts the accuracy of the pathloss calculation (and thus the determination of the initial transmit power for the RACH preamble) is an attenuation of the CPICH signal when the wireless device 14 is in a fading environment, or under a fading condition. In a fading environment, the wireless device 14 could calculate a high pathloss and consequently determine a high initial transmit power for transmission of the RACH preamble. Considering a case where there may not be an immediate dependency in uplink and downlink fading due to, e.g., timing differences at reception and transmission, the measured CPICH received signal code power may be in a deep fading condition at the receiver of the wireless device 14, while there may be not attenuation at the base station 12 when the wireless device 14 transmits the RACH preamble. In this case, initial transmit power for the RACH preamble may be significantly higher than it needs to be.

[0031] As discussed above, when transmitting the RACH preamble, the wireless device 14 ramps up from the determined initial transmit power for the RACH preamble until an AICH ACK/NACK is received or a predefined time-out period has expired. In, e.g., a fading environment, the wireless device 14 may determine a high initial transmit power for the RACH preamble. Further, the wireless device 14 may ramp-up the transmit power for the RACH preamble significantly before the RACH preamble is detected by the base station 12, and an AICH ACK is returned to the wireless device 14. As a result, the RACH message is transmitted at a high transmit power level and, in many cases, with a high SIR. This increases the Rise-over-Thermal (RoT) for the cell 16 (i.e., increases the uplink interference in the cell 16). Further, this increase in RoT (and thus uplink interference) becomes particularly problematic in a high load situation where many wireless devices 14 are attempting random access at the same time.

[0032] Embodiments of the present disclosure mitigate the increase in uplink interference caused by the conventional random access procedure described above. In particular, in some embodiments, the base station 12 detects a RACH preamble transmitted by one of the wireless devices 14. Rather than simply returning an AICH ACK if the SIR of the RACH preamble is greater than a threshold (and if sufficient hardware resources are available to decode the RACH message), the base station 12 determines whether one or more excessive received power conditions (e.g., RACH SIR greater than a predefined maximum SIR threshold and/or RoT greater than a predefined maximum RoT threshold) are met. If so, the base station 12 returns an AICH NACK to the wireless device 14. In this manner, the base station 12 prevents additional uplink interference that would have been caused by transmission of the RACH message by the wireless device 14. Thus, in other words, additional checks are performed by the base station 12 to determine whether to return an AICH ACK or an AICH NACK in such a manner as to block transmission of the RACH message when, e.g., RACH preamble SIR is high (to avoid transmission of a RACH message with high SIR) and/or RoT exceeds a predefined maximum RoT threshold (to lower RACH traffic at high RoT). Specifically, some embodiments disclosed herein address the problem of the wireless device 14 transmitting the RACH preamble with too high signal power and consequently also transmitting the RACH message with too high power. Similarly, some embodiments disclosed herein address the problem of the wireless device 14 transmitting the RACH preamble and the RACH message in a highly loaded cell scenario.

[0033] Figure 2 is a flow chart that illustrates the operation of the base station 12 according to one embodiment of the present disclosure. While this

embodiment is described with respect to the base station 12, this process may be performed by any suitable radio access node in the cellular RAN. This process is particularly relevant to embodiments in which the cellular RAN is a WRAN or some other suitable type of cellular RAN. As such, WRAN terminology is not used. However, this process is not limited to a WRAN. Note that while the flow chart of Figure 2 and the other flow charts or diagrams illustrate steps being performed in a particular order, the steps may be performed in any suitable order and are not limited to being performed in any particular order unless explicitly stated or otherwise required.

[0034] As illustrated, the base station 12 detects a random access attempt from one of the wireless devices 14 (step 100). In response, the base station 12 determines whether one or more excessive received power conditions are met (step 102). In one embodiment, the one or more excessive received power conditions are conditions that are indicative of: (a) high RoT which is indicative of a highly loaded cell scenario and/or (b) a high RACH SIR that will result in high uplink interference (e.g., transmission of the RACH message at high SIR) by the wireless device 14 if the base station 12 returns a positive ACK for the random access attempt. If the excess received power condition(s) are met, the base station 12 denies the random access attempt (step 104). In one embodiment, the base station 12 denies the random access attempt by returning a NACK for the random access attempt. In this manner, the base station 12 mitigates uplink interference by preventing the continuation of the random access attempt by the wireless device 14 (e.g., by preventing transmission of the RACH message). Conversely, if the excess received power condition(s) are not met, the base station 12 continues normal operation (step 106). For instance, in one embodiment, the base station 12 returns an ACK for the random access attempt if, e.g., a SIR associated with the random access attempt is greater than a predefined SIR threshold and there are sufficient hardware resources to handle the random access attempt (e.g., to decode the RACH message).

[0035] Figure 3 illustrates the operation of the base station 12 and one of the wireless devices 14 of Figure 1 according to one embodiment of the present disclosure. In this embodiment, the cellular RAN is a WRAN and, as such, WRAN terminology is sometimes used. However, this same process may be utilized in other suitable types of cellular RANs. Further, while this process is described with respect to the base station 12, this process is applicable to any radio access node. As illustrated, the wireless device 14 transmits a random access transmission (i.e., a RACH transmission). More specifically, the wireless device 14 starts the RACH transmission by selecting (e.g., randomly) a signature for a RACH preamble of the RACH transmission and selecting an initial transmit power level for the RACH preamble (steps 200 and 202). As discussed above, the wireless device 14 uses a known technique to determine the initial transmit power for the RACH preamble based on: (1 ) primary CPICH transmit power, (2) measured CPICH received signal code power, (3) uplink interference level in the cell 16, and (4) a constant value, i.e., an offset to be added in the calculation of the initial transmit power for the RACH preamble. The CPICH transmit power, the uplink interference, and the constant value are broadcast from the base station 12 to the wireless devices 14 in a broadcast channel. The wireless device 14 measures the CPICH received signal code power, which defines a pathloss for the CPICH signal from the base station 12 to the wireless device 14. In particular, the pathloss is the difference between the CPICH transmission power and the measured CPICH received signal code power. The wireless device 14 then transmits the signature for the RACH preamble at the initial transmit power (step 204).

[0036] The wireless device 14 continues the transmission of the RACH preamble by selecting (e.g., randomly) a next signature for the RACH preamble, increasing the transmit power for the RACH preamble, and transmitting the next signature of the RACH preamble at the increased transmit power (steps 206- 210). Transmission of the RACH preamble continues in this manner (steps 212- 216) until, in this example, the base station 12 detects the RACH preamble transmitted by the wireless device 14 (step 218). The base station 12

determines whether one or more excessive received power conditions are met, as discussed above. In particular, in this example, the base station 12 determines that the one or more excessive received power conditions are met (step 220). In response, the base station 12 returns an AICH NACK to the wireless device 14 (step 222). At that point, the wireless device 14 terminates the random access transmission (i.e., the wireless device 14 does not transmit the RACH message). In this manner, the base station 12 has prevented increased uplink interference that would have resulted from transmission of the RACH message by the wireless device 14.

[0037] Figure 4 is a flow chart that illustrates the operation of the base station 12 according to another embodiment of the present disclosure. In this embodiment, the cellular RAN is a WRAN and, as such, WRAN terminology is sometimes used. However, this same process may be utilized in other suitable types of cellular RANs. Further, while this process is described with respect to the base station 12, this process is applicable to any radio access node. As illustrated, the base station 12 detects a RACH preamble transmitted by one of the wireless devices 14 (step 300). Upon detecting the RACH preamble, the base station 12 estimates a SIR for the RACH preamble (step 302). This SIR is referred to herein as a RACH SIR. The RACH SIR can be estimated based on the detected RACH preamble using any suitable technique. For example, the detection of the RACH preamble is based on the signal amplitudes relative to the interference (noise) and, as such, the RACH SIR may be determined when detecting the RACH preamble.

[0038] The base station 12 then determines whether the estimated RACH SIR is greater than a predefined maximum SIR threshold (step 304). The predefined maximum SIR threshold may be, e.g., a constant or a configurable parameter. If the estimated RACH SIR is greater than the predefined maximum SIR threshold, the base station 12 sends an AICH NACK to the wireless device 14 (step 306). In this manner, the base station 12 prevents, or blocks, transmission of the RACH message by the wireless device 14, which in turn avoids an increase in RoT (or uplink interference) that would have been caused by transmission of the RACH message at a high SIR. Note that, in addition to considering the estimated RACH SIR, the base station 12 may, in some embodiments, consider one or more additional criteria related to uplink interference when deciding whether send the RACH NACK.

[0039] Returning to step 304, if the estimated RACH SIR is not greater than the predefined maximum SIR threshold, the base station 12 continues normal operation (step 308). For instance, in one embodiment, the base station 12 returns an AICH ACK to the wireless device 14 if, e.g., the estimated RACH SIR is greater than a predefined minimum SIR threshold (and less than the predefined maximum SIR threshold) and there are sufficient hardware resources available at the base station 12 to decode the subsequent transmission of the RACH message from the wireless device 14.

[0040] Figure 5 is a flow chart that illustrates the operation of the base station 12 according to another embodiment of the present disclosure. In this

embodiment, the cellular RAN is a WRAN and, as such, WRAN terminology is sometimes used. However, this same process may be utilized in other suitable types of cellular RANs. Further, while this process is described with respect to the base station 12, this process is applicable to any radio access node. As illustrated, the base station 12 detects a RACH preamble transmitted by one of the wireless devices 14 (step 400). In addition, the base station 12 determines a RoT measurement for the cell 16 (step 402). Uplink users in WCDMA share the same time-frequency resources, and they generate an interference rise above thermal noise at the receiver of the base station 12. This interference rise above thermal noise is known as "Rise-over-Thermal" or RoT. More generally, RoT is a ratio between a total interference received at the receiver of the base station 12 and thermal noise.

[0041 ] The base station 12 then determines whether the RoT for the cell 16 is greater than a predefined maximum RoT threshold (step 404). The predefined maximum RoT threshold may be, e.g., a constant or a configurable parameter. If the RoT is greater than the predefined maximum RoT threshold, the base station 12 sends an AICH NACK to the wireless device 14 (step 406). In this manner, the base station 12 prevents, or blocks, transmission of the RACH message by the wireless device 14, which in turn avoids an increase in RoT (or uplink interference) that would have been caused by transmission of the RACH message. Note that, in addition to considering the RoT, the base station 12 may, in some embodiments, consider one or more additional criteria related to uplink interference when deciding whether send the RACH NACK.

[0042] Returning to step 404, if the RoT is not greater than the predefined maximum RoT threshold, the base station 12 continues normal operation (step 408). For instance, in one embodiment, the base station 12 returns an AICH ACK to the wireless device 14 if, e.g., the RoT is greater than a predefined minimum RoT threshold and there are sufficient hardware resources available at the base station 12 to decode the subsequent transmission of the RACH message from the wireless device 14.

[0043] Figure 6 is a flow chart that illustrates the operation of the base station 12 according to another embodiment of the present disclosure. In this

embodiment, the cellular RAN is a WRAN and, as such, WRAN terminology is sometimes used. However, this same process may be utilized in other suitable types of cellular RANs. Further, while this process is described with respect to the base station 12, this process is applicable to any radio access node. As illustrated, the base station 12 detects a RACH preamble transmitted by one of the wireless devices 14 (step 500). Upon detecting the RACH preamble, the base station 12 estimates a SIR for the RACH preamble, as discussed above (step 502). In addition, the base station 12 determines the RoT for the cell 16, as also discussed above (step 504).

[0044] The base station 12 then determines whether the estimated RACH SIR is greater than a predefined maximum SIR threshold and the RoT for the cell 16 is greater than a predefined maximum RoT threshold (step 506). The predefined maximum SIR and RoT thresholds may be, e.g., constant values or configurable parameters. If the estimated RACH SIR is greater than the predefined maximum SIR threshold and the RoT for the cell 16 is greater than the predefined maximum RoT threshold, the base station 12 sends an AICH NACK to the wireless device 14 (step 508). In this manner, the base station 12 prevents, or blocks, transmission of the RACH message by the wireless device 14 when the cell 16 is already experiencing high uplink interference and transmission of the RACH message would be at high SIR. As a result, an increase in RoT (or uplink interference) that would have been caused by transmission of the RACH message at a high SIR is avoided. Note that, in addition to considering the estimated RACH SIR and RoT, the base station 12 may, in some embodiments, consider one or more additional criteria related to uplink interference when deciding whether send the RACH NACK.

[0045] Returning to step 506, if the estimated RACH SIR is not greater than the predefined maximum SIR threshold and/or if the RoT is not greater than the predefined maximum RoT threshold, the base station 12 continues normal operation (step 510). For instance, in one embodiment, the base station 12 returns an AICH ACK to the wireless device 14 if, e.g., the estimated RACH SIR is greater than a predefined minimum SIR threshold (and less than the predefined maximum SIR threshold) and there are sufficient hardware resources available at the base station 12 to decode the subsequent transmission of the RACH message from the wireless device 14.

[0046] In the embodiment of Figure 4, an AICH NACK is sent if the estimated RACH SIR is greater than the predefined maximum SIR threshold. In some embodiments, it may be desirable to not send an AICH NACK for all cases where the estimated RACH SIR is greater than the predefined maximum SIR threshold. For instance, there may be scenarios where one of the wireless devices 14 transmits a RACH preamble with a minimum transmit power and the estimated RACH SIR is still greater than the predefined maximum SIR threshold (e.g., when the wireless device 14 is close to and in line-of-sight of the base station 12). In this regard, Figure 7 is a flow chart that illustrates the operation of the base station 12 according to another embodiment of the present disclosure in which the base station 12 evaluates one or more additional criteria before sending an AICH NACK in response to detecting a RACH preamble with a high SIR. In this embodiment, the cellular RAN is a WRAN and, as such, WRAN terminology is sometimes used. However, this same process may be utilized in other suitable types of cellular RANs. Further, while this process is described with respect to the base station 12, this process is applicable to any radio access node.

[0047] As illustrated, the base station 12 detects a RACH preamble transmitted by one of the wireless devices 14 (step 600). Upon detecting the RACH preamble, the base station 12 estimates a SIR for the RACH preamble, as discussed above (step 602). The base station 12 then determines whether the estimated RACH SIR is greater than a predefined maximum SIR threshold (step 604). The predefined maximum SIR threshold may be, e.g., a constant value or a configurable parameter. If the estimated RACH SIR is greater than the predefined maximum SIR threshold, the base station 12 determines whether a RACH NACK should be sent (step 606). More specifically, the base station 12 determines whether one or more additional conditions, or criteria, are met for sending an AICH NACK. In one embodiment, the base station 12 determines that an AICH NACK is to be sent in order to block transmission of the RACH message if the signature for the detected RACH preamble is one of a set of RACH signatures that are to be blocked. For a WRAN, there are currently only 16 possible signatures. A subset of the signatures (preferably a proper subset that includes one or more but less than all of the 16 possible signatures) are predefined as signatures to be blocked. This subset includes one or more of the signatures. As such, if the signature used for the RACH preamble at the time of detection is one of the signatures to be blocked, the base station 12 determines that an AICH NACK is to be sent. Otherwise, an AICH NACK is not to be sent.

[0048] In another embodiment, the base station 12 is configured to block a predefined number or percentage of RACH preambles with high SIR (i.e., the estimated RACH SIR is greater than the predefined maximum SIR threshold). Thus, in step 606, the base station 12 determines whether an AICH NACK should be sent based on the predefined number or percentage of RACH preambles with high SIR to be blocked. As an example, the base station 12 may be configured to block 25% of RACH preambles with high SIR. In this case, the base station 12 may, e.g., be configured to block every fourth detected RACH preamble with high SIR. Thus, in step 606, the base station 12 may decide that an AICH NACK is to be blocked if the detected RACH preamble is the fourth RACH preamble with high SIR detected since last blocking a detected RACH preamble with high SIR. Note that the example above is only one example and is not intended to limit the scope of the present disclosure. One of ordinary skill in the art will appreciate that blocking of a predefined number or percentage of RACH preambles with high SIR may be implemented in many different ways.

[0049] If the base station 12 determines that an AICH NACK is to be sent, the base station 12 sends an AICH NACK to the wireless device 14 (step 608). In this manner, the base station 12 prevents, or blocks, transmission of the RACH message by the wireless device 14. As a result, an increase in RoT (or uplink interference) that would have been caused by transmission of the RACH message at a high SIR is avoided. Note that, in addition to considering the estimated RACH SIR and the criteria evaluated in step 606, the base station 12 may, in some embodiments, consider one or more additional criteria related to uplink interference when deciding whether send the RACH NACK.

[0050] Returning to steps 604 and 606, if the estimated RACH SIR is not greater than the predefined maximum SIR threshold or if the estimated RACH SIR is greater than the predefined maximum SIR threshold but the base station 12 determines that an AICH NACK is not to be sent, the base station 12 continues normal operation (step 610). For instance, in one embodiment, the base station 12 returns an AICH ACK to the wireless device 14 if, e.g., the estimated RACH SIR is greater than a predefined minimum SIR threshold (and less than the predefined maximum SIR threshold) and there are sufficient hardware resources available at the base station 12 to decode the subsequent transmission of the RACH message from the wireless device 14.

[0051] Figure 8 is a flow chart that illustrates the operation of the base station 12 according to another embodiment of the present disclosure in which the base station 12 evaluates one or more additional criteria before sending an AICH NACK in response to detecting a RACH preamble with a high SIR. This embodiment is substantially the same as that of Figure 7, but where the base station 12 checks RoT rather than RACH SIR. Note, however, that in another embodiment, the base station 12 may check both RACH SIR and RoT as in the embodiment of Figure 6. In the embodiment of Figure 8, the cellular RAN is a WRAN and, as such, WRAN terminology is sometimes used. However, this same process may be utilized in other suitable types of cellular RANs. Further, while this process is described with respect to the base station 12, this process is applicable to any radio access node.

[0052] As illustrated, the base station 12 detects a RACH preamble transmitted by one of the wireless devices 14 (step 700). Upon detecting the RACH preamble, the base station 12 determines a RoT for the cell 16, as discussed above (step 702). The base station 12 then determines whether the RoT for the cell 16 is greater than a predefined maximum RoT threshold (step 704). The predefined maximum RoT threshold may be, e.g., a constant value or a configurable parameter. If the RoT is greater than the predefined maximum RoT threshold, the base station 12 determines whether a RACH NACK should be sent (step 706). More specifically, the base station 12 determines whether one or more additional conditions, or criteria, are met for sending an AICH NACK. In one embodiment, the base station 12 determines that an AICH NACK is to be sent in order to block transmission of the RACH message if the signature for the detected RACH preamble is one of a set of RACH signatures that are to be blocked. For a WRAN, there are currently only 16 possible signatures. A subset of the signatures (preferably a proper subset that includes one or more but less than all of the 16 possible signatures) are predefined as signatures to be blocked. This subset includes one or more of the signatures. As such, if the signature used for the RACH preamble at the time of detection is one of the signatures to be blocked, the base station 12 determines that an AICH NACK is to be sent. Otherwise, an AICH NACK is not to be sent. [0053] In another embodiment, the base station 12 is configured to block a predefined number or percentage of RACH preambles in general, or in some embodiments, a predefined number or percentage of RACH preambles with high SIR (i.e., RACH SIR greater than the predefined maximum SIR threshold). Thus, in step 706, the base station 12 determines whether an AICH NACK should be sent based on the predefined number or percentage of RACH preambles (in some embodiments with high SIR) to be blocked. As an example, the base station 12 may be configured to block 25% of RACH preambles with high SIR. In this case, the base station 12 may, e.g., be configured to block every fourth detected RACH preamble with high SIR. Thus, in step 706, the base station 12 may decide that an AICH NACK is to be blocked if the detected RACH preamble is the fourth RACH preamble with high SIR detected since last blocking a detected RACH preamble with high SIR. Note that the example above is only one example and is not intended to limit the scope of the present disclosure. One of ordinary skill in the art will appreciate that blocking of a predefined number or percentage of RACH preambles with high SIR may be implemented in many different ways.

[0054] If the base station 12 determines that an AICH NACK is to be sent, the base station 12 sends an AICH NACK to the wireless device 14 (step 708). In this manner, the base station 12 prevents, or blocks, transmission of the RACH message by the wireless device 14. As a result, an increase in RoT (or uplink interference) that would have been caused by transmission of the RACH message is avoided. Note that, in addition to considering the RoT and the criteria evaluated in step 706, the base station 12 may, in some embodiments, consider one or more additional criteria related to uplink interference when deciding whether send the RACH NACK.

[0055] Returning to steps 704 and 706, if the RoT is not greater than the predefined maximum RoT threshold or if the RoT is greater than the predefined maximum RoT threshold but the base station 12 determines that an AICH NACK is not to be sent, the base station 12 continues normal operation (step 710). For instance, in one embodiment, the base station 12 returns an AICH ACK to the wireless device 14 if, e.g., the RoT is greater than a predefined minimum RoT threshold (and less than the predefined maximum RoT threshold) and there are sufficient hardware resources available at the base station 12 to decode the subsequent transmission of the RACH message from the wireless device 14.

[0056] While the base station 12 (or any type of radio access node) may be implemented in hardware or any combination of hardware and/or software, Figure 9 is a block diagram of the base station 12 according to one embodiment of the present disclosure. Note that while the base station 12 is discussed herein, the functionality of the base station 12 described herein can be performed by any type of radio access node. As illustrated, the base station 12 includes a baseband unit 18 including a processor 20, memory 22, and a network interface 24 and a radio unit 26 including a transceiver 28 coupled to one or more antennas 30. In one embodiment, the functionality of the base station 12 described herein is implemented in software stored in the memory 22 and executed by the processor 20. Additionally, the base station 12 may include additional components responsible for providing additional functionality, including any of the functionality described above and/or any functionality necessary to support the embodiments described herein.

[0057] In one embodiment, a computer program including instructions which, when executed by at least one processor (e.g., the processor 20), causes the at least one processor to carry out the functionality of the base station 12 according to any one of the embodiments described herein is provided. In one

embodiment, a carrier containing the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as the memory 22).

[0058] Figure 10 is a functional block diagram of the base station 12 according to one embodiment of the present disclosure. As illustrated, the base station 12 includes a random access attempt detection module 32, a

determination module 34, and a communication module 36, each of which is implemented in software. The random access attempt detection module 32 is operative to detect a random access attempt (e.g., a RACH preamble transmission) of a wireless device 14. The determination module 34 is operative to decide whether to accept the random access attempt (e.g., decide to send an AICH ACK) or deny the random access attempt (e.g., decide to send an AICH NACK) according to any one of the embodiments described herein. The communication module 36 is operative to send the random access attempt acceptance (e.g., AICH ACK) or denial (e.g., AICH NACK) to the wireless device 14, as discussed above.

[0059] The following acronyms are used throughout this disclosure.

• 3GPP Third Generation Partnership Project

• ACK Acknowledgement

• AICH Acquisition Indicator Channel

• CPICH Common Pilot Channel

• dB Decibel

• ms Millisecond

• NACK Negative Acknowledgement

• RACH Random Access Channel

• RAN Radio Access Network

• RoT Rise-over-Thermal

• SIR Signal-to-lnterference Ratio

• UTRAN Universal Terrestrial Radio Access Network

• WCDMA Wideband Code Division Multiple Access

• WRAN Wideband Code Division Multiple Access Radio

Access Network

[0060] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.

Claims

Claims What is claimed is:

1 . A method of operation of a radio access node (12) in a cellular

communications network (10), comprising:

detecting a random access attempt made by a wireless device (14);

determining whether one or more conditions indicative of an excessive received power condition are satisfied; and

if the one or more conditions are satisfied, sending a denial of the random access attempt to the wireless device (14).

2. The method of claim 1 wherein the one or more conditions comprise a condition that a Signal-to-lnterference Ratio, SIR, for the random access attempt is greater than a predefined SIR threshold.

3. The method of any one of claims 1 - 2 wherein the one or more conditions comprise a condition that a Rise-over-Thermal, RoT, for a cell (16) served by the radio access node (12) for which the random access attempt is made is greater than a predefined RoT threshold.

4. The method of claim 1 wherein detecting the random access attempt comprises detecting a Random Access Channel, RACH, preamble.

5. The method of claim 4 wherein the one or more conditions comprise a condition that a Signal-to-lnterference Ratio, SIR, for the RACH preamble is greater than a predefined SIR threshold.

6. The method of any one of claims 4 - 5 wherein the one or more conditions comprise a condition that a Rise-over-Thermal, RoT, for a cell (16) served by the radio access node (12) for which the random access attempt is made is greater than a predefined RoT threshold.

7. The method of any one of claims 4 - 6 further comprising: determining whether one or more conditions for sending a denial of the random access attempt to the wireless device (14) are satisfied;

wherein sending the denial of the random access attempt to the wireless device (14) comprises sending the denial of the random access attempt to the wireless device (14) if the one or more conditions indicative of the excessive received power condition are satisfied and the one or more conditions for sending the denial of the random access attempt to the wireless device (14) are satisfied.

8. The method of claim 7 wherein the one or more conditions for sending the denial of the random access attempt comprise a condition that a signature detected in the RACH preamble be one of a subset of possible signatures for which random access attempts are to be denied.

9. The method of claim 7 wherein the one or more conditions for sending the denial of the random access attempt comprise a condition that a predefined percentage of random access attempts are to be denied when a cell load of the cell (16) served by the radio access node (12) for which the random access attempt is made is greater than a predefined threshold.

10. The method of any one of claims 4 - 9 wherein sending the denial of the random access attempt to the wireless device (14) comprises sending an Acquisition Indicator Channel, AICH, Negative Acknowledgment, NACK, to the wireless device (14).

1 1 . The method of any one of claims 1 - 10 wherein the cellular

communications network (10) is a Wideband Code Division Multiple Access, WCDMA, cellular communications network.

12. A radio access node (12) for a cellular communications network (10), comprising:

a transceiver (28);

a processor (20) associated with the transceiver (28); and

memory (22) containing software instructions executable by the processor (20) whereby the radio access node (12) is operative to:

detect a random access attempt made by a wireless device (14); determine whether one or more conditions indicative of an excessive received power condition are satisfied; and

if the one or more conditions are satisfied, send a denial of the random access attempt to the wireless device (14).

13. A radio access node (12) for a cellular communications network (10) adapted to:

detect a random access attempt made by a wireless device (14);

determine whether one or more conditions indicative of an excessive received power condition are satisfied; and

14. The radio access node (12) of claim 13 further adapted to perform the method of any one of claims 2 - 1 1 .

15. A radio access node (12) for a cellular communications network (10) comprising:

means for detecting a random access attempt made by a wireless device

(14);

means for determining whether one or more conditions indicative of an excessive received power condition are satisfied; and

means for sending a denial of the random access attempt to the wireless device (14) if the one or more conditions are satisfied.

16. A computer program comprising instructions which, when executed on at least one processor (20), cause the at least one processor (20) to carry out the method according to any one of claims 1 - 1 1 .

17. A carrier containing the computer program of claim 16 wherein the carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium.

18. A radio access node (12) for a cellular communications network (10) comprising:

a random access attempt detection module (32) operative to detect a random access attempt made by a wireless device (14);

a determination module (34) operative to determine whether one or more conditions indicative of an excessive received power condition are satisfied; and a communication module (36) operative to send a denial of the random access attempt to the wireless device (14) if the one or more conditions are satisfied.