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WO1999065166A2 - Systeme de telecommunication sans fil utilisant un intervalle de temps a modulation coherente et presentant un champ a modulation differentielle (cdvcc) constituant des symboles pilotes utiles pour l'estimation de voies - Google Patents

Systeme de telecommunication sans fil utilisant un intervalle de temps a modulation coherente et presentant un champ a modulation differentielle (cdvcc) constituant des symboles pilotes utiles pour l'estimation de voies Download PDF

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Publication number
WO1999065166A2
WO1999065166A2 PCT/EP1999/003954 EP9903954W WO9965166A2 WO 1999065166 A2 WO1999065166 A2 WO 1999065166A2 EP 9903954 W EP9903954 W EP 9903954W WO 9965166 A2 WO9965166 A2 WO 9965166A2
Authority
WO
WIPO (PCT)
Prior art keywords
time slot
modulated
symbol sequence
differentially
predetermined symbol
Prior art date
Application number
PCT/EP1999/003954
Other languages
English (en)
Other versions
WO1999065166A3 (fr
Inventor
Risto Paatelma
Original Assignee
Nokia Mobile Phones Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nokia Mobile Phones Limited filed Critical Nokia Mobile Phones Limited
Priority to AU52797/99A priority Critical patent/AU5279799A/en
Publication of WO1999065166A2 publication Critical patent/WO1999065166A2/fr
Publication of WO1999065166A3 publication Critical patent/WO1999065166A3/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation

Definitions

  • This invention relates generally to radiotelephones and, in particular, to radiotelephones or mobile stations such as those capable of operation with a digital wireless communication network.
  • Fig. 1 A, 1 B and 1 C show the frame and time slot formats for an exemplary prior art digital Time Division Multiple Access (TDMA) cellular air interface known in the art as IS-136 (see, for example, IS-136.1, Rev. A, 3/21/96 and IS-136.2, Rev. A, 2/12/1996, as well as later revisions).
  • TDMA Time Division Multiple Access
  • Fig. 1A shows that a 40 millisecond frame consists of six time slots. Slots 1-3 and 4-6 each comprise one TDMA Block. In the forward direction from a base station to a mobile station the frames are continuously transmitted. A given mobile station is assigned to receive in one time slot per frame for a half data rate case, and is assigned to receive in two time slots for a full data rate case.
  • Fig. 1B illustrates the format of one slot in the direction from the mobile station to the base station
  • Fig. 1C illustrates the format of one slot in the direction from the base station to the mobile station.
  • the base station forms a part of a Base Station/Mobile Switching Center/I nterworking function (BMI).
  • BMI Base Station/Mobile Switching Center/I nterworking function
  • CDVCC Coded Digital Verification Color Code
  • DVCC Digital Verification Color Code
  • DTC digital traffic channel
  • a DVCC of 8-bits is coded with a (15,11 ) Hamming code shortened to (12,8), giving a CDVCC of 12-bits.
  • the CDVCC is decoded and compared to a previously received and stored DVCC.
  • the modulation scheme uses the ⁇ /4-shifted DQPSK constellation shown in Fig. 1D.
  • Gray code is used in the mapping; i.e., two di-bit symbols corresponding to adjacent signal phases differ only in a single bit. Since most probable errors due to noise result in the erroneous selection of an adjacent phase, most di-bit symbol errors contain only a single bit error. Note the rotation by ⁇ r/4 of the basic QPSK constellation for odd (denoted ⁇ ) and even (denoted ⁇ 8>) symbols.
  • the information is differentially encoded and symbols are transmitted as changes in phase rather than absolute phases.
  • the binary data stream (b enters the modulator and is converted by a serial-to-parallel converter into two separate binary streams (X k ) and (Y k ). Starting from bit 1 in time of stream b m , all odd numbered bits form stream X k and all even numbered bits form stream Y k .
  • TIA IS-136, Rev. C TIA IS-136, Rev. C
  • 8PSK coherently modulated pilot symbol sequences are defined per time slot.
  • Fig. 1 E illustrates a currently proposed slot format.
  • Each pilot symbol sequence consists of three symbols.
  • the CDVCC field can be used to determine the channel quality.
  • the proposed 8PSK slot format these symbols were removed at least on part to increase the gross or maximum bit rate, and because of a channel estimation and detection problem that arose. Since the CDVCC symbols are not reserved in the proposed slot format, this enables the transmission of data bits instead of the CDVCC bits.
  • the channel estimation/detection problem is as follows.
  • the coherent (e.g., 8PSK) receiver requires that a channel estimation be performed. However, if the predetermined CDVCC symbols are first used to make the channel estimation, and the CDVCC sequence is then detected using this channel estimation, the result is highly biased. More generally, if in the channel estimation the coherent receiver assumes that sequence d was transmitted, and if then the decision is made based on this channel estimation, the decision will more likely yield the sequence d than some other sequence. In any event, reliable information regarding the amount of interference in the channel is not obtained.
  • a method of this invention for operating a wireless mobile or user station to receive a time slot sent through a radio channel from a transmitter, the time slot being coherently modulated except for a portion that contains a predetermined symbol sequence that is differentially modulated.
  • a next step differentially detects the portion of the received time slot that is comprised of the predetermined symbol sequence.
  • a further step of the method operates to perform a channel estimation for a coherent detector used to detect the other portions of the time slot.
  • the predetermined symbol sequence is modulated in accordance with a differential phase shift technique, such as Differential Quadrature Phase Shift Keying (DQPSK), Differential 8 Phase Shift Keying (D8PSK), ⁇ /4-shifted DQPSK, or 16 level DQPSK.
  • DQPSK Differential Quadrature Phase Shift Keying
  • D8PSK Differential 8 Phase Shift Keying
  • ⁇ /4-shifted DQPSK ⁇ /4-shifted DQPSK
  • 16 level DQPSK 16 level DQPSK.
  • first and fourth occurring symbol sequences within a time slot are differentially modulated using DQPSK
  • the second and third occurring symbol sequences are differentially modulated using D8PSK.
  • all of the symbol sequence occurrences are differentially modulated using D8PSK.
  • the portion of the time slot that is differentially modulated is a CDVCC/PILOT field, while the data fields and any other fields are modulated using 8PSK.
  • Figs. 1A, 1 B and 1C depict the frame and time slot formats for an exemplary prior art TDMA air interface
  • Fig. 1D illustrates the ⁇ /4 shifted DQPSK phase constellation used by the exemplary prior art TDMA air interface
  • Fig. 1E depicts a proposed forward link slot format for use in a coherently modulated (8PSK) TDMA air interface
  • Fig. 2 is a block diagram of a mobile station that is constructed and operated in accordance with this invention.
  • Fig. 3 is an elevational view of the mobile station shown in Fig. 2, and which further illustrates a cellular communication system to which the mobile station is bidirectionally coupled through wireless RF links;
  • Figs. 4A and 4B each depict an embodiment of a pilot symbol structure in accordance with this invention, wherein Fig. 4A depicts a DQPSK CDVCC/PILOT for the first and last pilot sequences shown in Fig. 1 E, and Fig. 4B depicts a D8PSK CDVCC/PILOT, or the middle pilot sequences if the DQPSK technique of Fig. 4A is employed; and
  • Fig. 5 is a diagram that is useful in explaining how the pilot symbols are modulated in accordance with one exemplary embodiment of this invention, wherein a pilot block includes three symbols, where a first symbol is a phase reference, and the second and third symbols encode two bits each using DQPSK.
  • a wireless user terminal or mobile station 10 such as but not limited to a cellular radiotelephone or a personal communicator, that is suitable for practicing this invention.
  • the mobile station 10 includes an antenna 12 for transmitting signals to and for receiving signals from a base site or base station 30.
  • the base station 30 is a part of a cellular network comprising the Base Station/Mobile Switching Center/I nterworking function (BMI) 32 that includes a mobile switching center (MSC) 34.
  • BMI Base Station/Mobile Switching Center/I nterworking function
  • MSC mobile switching center
  • the mobile station includes a modulator (MOD) 14A, a transmitter 14, a receiver 16, a demodulator (DEMOD) 16A, and a controller 18 that provides signals to and receives signals from the transmitter 14 and receiver 16, respectively.
  • These signals include signalling information in accordance with the air interface standard of the applicable cellular system, and also user speech and/or user generated data.
  • the air interface standard is assumed for this invention to include a physical and logical frame and time slot structure, although the teaching of this invention is not intended to be limited for use only in TDMA type systems.
  • the controller 18 also includes the circuitry required for implementing the audio and logic functions of the mobile station.
  • the controller 18 may be comprised of a digital signal processor device, a microprocessor device, and various analog to digital converters, digital to analog converters, and other support circuits.
  • the control and signal processing functions of the mobile station are allocated between these devices according to their respective capabilities.
  • the controller 18 is assumed to contain or implement a differential CDVCC/PILOT detector 18a, as described in further detail below, as well as a coherent (e.g., 8PSK) detector 18b for detecting the data and other fields of received time slots.
  • the coherent detector 18b requires that a channel estimation be performed.
  • differentially modulated CDVCC/PILOT sequences are detected by the differential detector 18a, and an approximate estimation of channel quality is obtained. Since the CDVCC/PILOT sequences are known a priori, the coherent detector 18b can reconstruct the transmitted signal and thereby estimate the channel. The data fields are then detected by the coherent detector, using the obtained channel estimation. The problem of generating a biased estimation of the channel is thus overcome.
  • a user interface includes a conventional earphone or speaker 17, a conventional microphone 19, a display 20, and a user input device, typically a keypad 22, all of which are coupled to the controller 18.
  • the keypad 22 includes the conventional numeric (0-9) and related keys (#,*) 22a, and other keys 22b used for operating the mobile station 10.
  • the mobile station 10 also includes a battery 26 for powering the various circuits that are required to operate the mobile station.
  • the mobile station 10 also includes various memories, shown collectively as the memory 24, wherein are stored a plurality of constants and variables that are used by the controller 18 during the operation of the mobile station.
  • the mobile station 10 can be a vehicle mounted or a handheld device. It should further be appreciated that the mobile station 10 can be capable of operating with one or more air interface standards, modulation types, and access types.
  • the inventor has realized that the symbol (bit) error probability of the CDVCC bits is independent of the channel estimation if these bits are differentially detected.
  • the coherent detector that is used for the detection of the data and other fields of the time slot can, however, calculate the phase of these symbols, and it can use these symbols as a pilot sequence. While coherent modulation requires the use of pilot tones or symbols, a differentially encoded CDVCC, when used as a pilot sequence, does not adversely affect the bit rate (the number of data symbols).
  • the transmitter of the base station 30 is assumed to be capable of transmitting most of the time slot modulated using the 8PSK constellation, and for transmitting the CDVCC portion modulated using some type of differential phase shift constellation, such as a DQPSK or a D8PSK constellation.
  • the modulation of the CDVCC could also be, by example, ⁇ /4-shifted DQPSK, as shown in Fig. 1D, or even 16 level differential phase shift modulation.
  • the method in accordance with this invention thus enables one to obtain the benefits of the current CDVCC technique, wherein a bit error rate measurement can be derived from the CDVCC sequences, for use in making the channel quality estimation. Since the pilot symbols are being employed for this purpose, which must be present in any case for use by the coherent modulator/demodulator, the maximum data transfer rate of the channel is not adversely affected.
  • Figs. 4A and 4B each depict an embodiment of a pilot symbol structure in accordance with this invention, wherein Fig. 4A depicts a DQPSK CDVCC/PILOT for the first and last pilot sequences (i.e. PILOT-1 and PILOT-4) shown in Fig. 1E, and Fig. 4B depicts a D8PSK CDVCC/PILOT that can be used for all four pilot sequences, or for the middle two pilot sequences (i.e., PILOT-2 and PILOT-3) if the DQPSK technique of Fig. 4A is employed for the first and last sequences.
  • the phase reference for the differentially coded CDVCC/PILOT field is the first pilot symbol, which is set to a value of, by example, 1+j0 (phase 0°).
  • the transmitted signal (slot) has the format:
  • P n is the Pilot/CDVCC symbol sequence modulated from bits p. These sequences are differentially modulated, the bits p are beforehand known in the receiver, D n is the coherently modulated data sequence, and at least one symbol of each pilot sequence is beforehand known in the receiver.
  • the receiver differentially detects the Pilot/CDVCC sequences. As a result the symbol decision ⁇ n or bit decisions p can be made. The channel quality estimation is made based on these decisions, such as comparing decided bits p to transmitted bits p. It should be noted that for this detection the receiver does not utilize knowledge of the bits p.
  • the data sequences D n must be coherently detected due to the coherent modulation used in these sequences. This implies that the receiver inherently requires a channel estimation c. While the phase of at least one symbol in each Pilot/CDVCC sequences P n is predetermined, the receiver can exactly calculate the transmitted symbols of each Pilot/CDVCC sequences P n (which are differentially modulated). With the aid of the exactly known symbols P n the receiver is able to calculate the channel estimation c, and with the aid of the calculated estimation the data sequences D ⁇ can be coherently detected.
  • pilot symbols are modulated with ⁇ /4-shifted DQPSK with the following phase shifts: 00 ⁇ /4
  • the encoder transmits the CDVCC bits in the pilot sequence consisting of 3 symbols, wherein the first symbol is defined to always be 1 +0j.
  • symbol_0 1+0j
  • the exact phase values can be calculated.
  • the CDVCC sequence can be used for coherent channel estimation, which is a desired result.
  • the base station 30 will also include a suitable differential demodulator, and the mobile station 10 a suitable differential modulator.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

L'invention concerne un procédé de fonctionnement d'une station mobile ou d'utilisateur sans fil pour recevoir un intervalle de temps envoyé par une voie radio à partir d'un émetteur. Cet intervalle de temps présente une modulation cohérente sauf dans une partie qui contient une séquence de symboles prédéterminés qui est modulée de manière différentielle. Dans une étape suivante, on détecte la partie de l'intervalle de temps reçu qui contient la séquence de symboles prédéterminés. Une autre étape assure le fonctionnement d'une estimation de voie pour un détecteur cohérent qui est utilisé pour détecter d'autres parties de l'intervalle de temps. Par exemple, la séquence de symboles prédéterminés est modulée en fonction d'une modulation par déplacement de phase en quadrature différentielle (DQPSK), ou d'une modulation par déplacement de phase 8 différentielle (D8PSK), ou DQPSK par déplacement π/4, ou DQPSK à 16 niveaux. Dans un mode de réalisation préféré, la partie de l'intervalle de temps qui est modulée de manière différentielle est un champ CDVCC/PILOT tandis que les champs de données et d'autres champs sont modulés par 8PSK.
PCT/EP1999/003954 1998-06-08 1999-06-08 Systeme de telecommunication sans fil utilisant un intervalle de temps a modulation coherente et presentant un champ a modulation differentielle (cdvcc) constituant des symboles pilotes utiles pour l'estimation de voies WO1999065166A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU52797/99A AU5279799A (en) 1998-06-08 1999-06-08 Wireless telecommunications system employing a coherently modulated time slot having a differentially modulated field (cdvcc) providing pilot symbols useful forchannel estimation

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US8839698P 1998-06-08 1998-06-08
US60/088,396 1998-06-08
US32613499A 1999-06-04 1999-06-04
US09/326,134 1999-06-04

Publications (2)

Publication Number Publication Date
WO1999065166A2 true WO1999065166A2 (fr) 1999-12-16
WO1999065166A3 WO1999065166A3 (fr) 2000-01-20

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PCT/EP1999/003954 WO1999065166A2 (fr) 1998-06-08 1999-06-08 Systeme de telecommunication sans fil utilisant un intervalle de temps a modulation coherente et presentant un champ a modulation differentielle (cdvcc) constituant des symboles pilotes utiles pour l'estimation de voies

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AU (1) AU5279799A (fr)
WO (1) WO1999065166A2 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2380103A (en) * 2001-06-29 2003-03-26 Sepura Ltd TETRA communications system using a differential 8PSK (or D8PSK) modulation method

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE69224687T2 (de) * 1991-07-30 1998-07-02 Nippon Electric Co Trägerfrequenz-Fehlerdetektorschaltung zur genauen Feststellung eines Trägerfrequenzfehlers
US5544156A (en) * 1994-04-29 1996-08-06 Telefonaktiebolaget Lm Ericsson Direct sequence CDMA coherent uplink detector
US5809083A (en) * 1994-11-23 1998-09-15 At&T Wireless Services, Inc. Differentially encoded pilot word system and method for wireless transmissions of digital data

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2380103A (en) * 2001-06-29 2003-03-26 Sepura Ltd TETRA communications system using a differential 8PSK (or D8PSK) modulation method
GB2380103B (en) * 2001-06-29 2004-05-19 Sepura Ltd Communications systems

Also Published As

Publication number Publication date
AU5279799A (en) 1999-12-30
WO1999065166A3 (fr) 2000-01-20

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