CN1845472A - OFDM single antenna reception diversity technology - Google Patents

Abstract

The invention related to OFDM technique applies only one space channel to construct multiple channel frequency response for diversity treatment. Wherein, first multiplying varied-frequency discrete imaginary index signal to the baseband complex time domain sequence to obtain multiplex complex time domain sequence; then taking FFT to obtain multiplex frequency-domain sequence; applying same guide-frequency sequence for channel estimation to every frequency- domain sequence to obtain the objective response sequence for diversity treatment. This invention has wide application.

Description

The OFDM single antenna reception diversity technology

Technical field

Technical field under the technical solution of the present invention is OFDM (OFDM) technology in the radio communication.

Background technology

OFDM (OFDM) technology is generally believed it is the one preferred technique of broadband wireless communications.Although the OFDM technology can suppress the intersymbol interference in the time domain effectively, the frequency selective fading of channel has restricted the further raising of OFDM performance equally.The space diversity reception to communicate of many antennas can improve the performance of ofdm system effectively, can be restricted but in most cases at portable terminal a plurality of antennas are installed.Diversity technique comprises reception diversity technology and transmit diversity techniques between multi-antenna space, and reception diversity technology needs two antennas at least at receiving terminal, and transmit diversity techniques needs two antennas at least at transmitting terminal.The OFDM single antenna reception diversity technology that the present invention proposes both had been different from transmit diversity techniques, also was different from the reception diversity technology of many antennas.The OFDM single antenna reception diversity technology only utilizes one road space channel just can construct a plurality of channel frequency responses and realizes the diversity processing.The OFDM single antenna reception diversity technology can also be united use with existing transmit diversity techniques, also can use with existing multi-antenna receive diversity technical tie-up, further improves the performance of ofdm system.The present invention can be applicable to systems such as ground digital television broadcast, ground digital audio broadcasting, wideband wireless local area network, the 4th third-generation mobile communication.

Summary of the invention

In most of the cases, special in the application that is ground digital television broadcast, ground digital audio broadcasting, macrocell mobile communication, the decline of serious frequency selectivity can appear in broadband wireless channel, and this has limited the further raising of ofdm system performance.The space diversity reception to communicate of many antennas can alleviate the influence of selectivity of channel frequency decline, and diversity technique comprises reception diversity technology and transmit diversity techniques between multi-antenna space.

Adopt reception diversity technology existing application widely in wireless communication system of a plurality of antennas at receiving terminal.Transmit diversity is meant emission " identical information " on different antennas (signal form may be different, launch time, frequency difference), needs a reception antenna at least at receiving terminal, just can obtain emission diversity gain.Physically just there is the multichannel space channel in diversity system between multi-antenna space, and transmit diversity techniques adopts a plurality of transmitting antennas to increase the quantity of space channel at transmitting terminal, and reception diversity technology adopts a plurality of reception antennas to increase the quantity of space channel at receiving terminal.

The OFDM single antenna reception diversity technology only utilizes one road space channel just can construct a plurality of channel frequency responses and realizes the diversity processing.In ofdm system, to realize the single antenna reception diversity processing, construct a plurality of channel frequency response sequences with regard to handy signal processing method.How to construct a plurality of channel frequency response sequences, the present invention has provided following technical scheme.

In the OFDM receiving system, at first carry out radio frequency (RF) demodulation and obtain the multiple time domain sequences of base band, remove protection at interval after (GI), the multiple time domain sequences of base band be multiply by the discrete time imaginary exponent signal of different frequency respectively, obtain the multiple time domain sequences of multichannel.Again the multiple time domain sequences in every road is carried out fast Fourier transform (FFT) respectively, obtain the multichannel frequency domain sequence.Respectively every road frequency domain sequence is carried out channel estimating with same pilot frequency sequence, then can obtain the frequency response sequence of multichannel diversity channel.Utilize the frequency response sequence of a plurality of diversity channels, just can carry out diversity and handle the multichannel frequency domain sequence.

Below explain the theoretical foundation of OFDM single antenna reception diversity technology.The multiple time domain sequences of base band be multiply by discrete time imaginary exponent signal, and the frequency domain sequence behind the FFT will produce circular shifting.The frequency difference of the discrete time imaginary exponent signal that the multiple time domain sequences of base band be multiply by, the circumferential displacement amount difference that frequency domain sequence produces.The frequency response sequence of the multichannel diversity channel that technical solution of the present invention produces is the different circular shifting duplicates of the same space channel frequency response sequence in essence.For frequency selective fading channels, the channel frequency response sequence has fluctuating, correlation between the frequency response of the more different frequency of frequency difference is lower, therefore the frequency response sequence of different displacements can provide diversity to each other mutually, therefore can be constructed the frequency response sequence of multichannel diversity channel by one road space channel.Can carry out the OFDM single antenna reception diversity on this basis handles.

No matter diversity technique between existing multi-antenna space is transmit diversity techniques or multi-antenna receive diversity technology, all needs to adopt a plurality of antennas could realize the diversity processing.The OFDM single antenna reception diversity technology that the present invention proposes only need adopt an antenna just can realize the diversity processing at receiving terminal.With respect to the space diversity reception to communicate of many antennas, the OFDM single antenna reception diversity technology can make the realization of receiving system simpler, particularly is being difficult for installing under the situation of a plurality of antennas, and the present invention is just more meaningful.

Description of drawings

Accompanying drawing has provided the realization block diagram of OFDM single antenna reception diversity technology.The frequency response sequence H of all diversity channels in the accompanying drawing _i(k), k=0,1 ..., N-1, i=0,1 ..., D-1 is based on that same pilot frequency sequence estimates, and pilot frequency sequence is not done any shifting processing.

Embodiment

At first carry out radio frequency (RF) demodulation, remove protection and obtain the multiple time domain sequences of base band after (GI) at interval, with y (n) expression, wherein n express time sequence number.Y (n) be multiply by the discrete time imaginary exponent signal e of different frequency respectively ^{J2 π in/D}(or e ^{-j2 π in/D}), i=0,1 ..., D-1 obtains the multiple time domain sequences of multichannel

y _i(n)=y (n) e ^{J2 π in/D}(or y _i(n)=y (n) e ^{-j2 π in/D}), i=0,1 ..., D-1

Wherein D is a diversity quantity, and span is reference with the channel impulse response length.Discrete time frequency quantity in the above-mentioned formula (or I=0,1 ..., D-1 has adopted the strategy that waits stepping, and initial frequency is zero.Certainly, the discrete time frequency quantity also can adopt the non-strategy that waits stepping.When initial frequency is got The discrete time frequency quantity of stepping such as a group is

I=0,1 ..., D-1; When initial frequency is got The discrete time frequency quantity of stepping such as a group is I=0,1 ..., D-1.The vague generalization algorithm of one group of discrete time frequency quantity is

I=0,1 ..., D-1, ω _iD frequency for any continuous 2 π intervals.

Then to every road y _i(n), i=0,1 ..., D-1 goes here and there respectively and conversion, fast Fourier transform (FFT), obtains multichannel frequency domain sequence Y _i(k), k=0,1 ..., N-1, i=0,1 ..., D-1, wherein N is the number of subcarriers of ofdm system, k represents the subcarrier sequence number.Respectively the frequency response sequence of every road diversity channel is estimated based on same pilot frequency sequence, obtained the frequency response sequence H of multichannel diversity channel _i(k), k=0,1 ..., N-1, i=0,1 ..., behind the D-1, just can carry out diversity and handle the multichannel frequency domain sequence.

The diversity Processing Algorithm can adopt selective diversity algorithm or high specific combination (MRC) diversity algorithm.Press the selective diversity algorithm, the output sequence of frequency domain is

$Y\left(k\right)=Y_i\left(k\right){|}_{\max \left\{\right|H_i\left(k\right)\left|\right\}},$ i＝0，1，…，D-1

The i.e. output Y (k) of the frequency domain sequence on each frequency, k=0,1 ..., N-1, all diversity channel of selective channel frequency response mould value maximum output.Through frequency domain channel equalization, the frequency domain sequence that obtains launching

$X\left(k\right)=\frac{Y\left(k\right)}{\max \left\{\right|H_i\left(k\right)|,i=\mathrm{0,1},\·\·\·,D-1\}},$ k＝0，1，…，N-1

Press the MRC diversity algorithm, through frequency domain channel equalization, the frequency domain sequence that obtains launching

$X\left(k\right)=\frac{\underset{i=0}{\overset{D-1}{\mathrm{\Σ}}}{H}_i^{*}\left(k\right)Y_i\left(k\right)}{\underset{i=0}{\overset{D-1}{\mathrm{\Σ}}}{\left|H_i\left(k\right)\right|}^2},$ k＝0，1，…，N-1

Wherein * represents conjugate operation.

Claims (1)

1. Preamble

   Subject name: OFDM single antenna reception diversity technology.With the immediate prior art of subject matter: multi-antenna receive diversity technology and transmit diversity techniques.No matter be multi-antenna receive diversity technology or transmit diversity techniques, all need to adopt a plurality of antennas could realize the diversity processing.The multi-antenna receive diversity technology adopts a plurality of reception antennas could realize the diversity processing at receiving terminal, and transmit diversity techniques adopts a plurality of transmitting antennas could realize the diversity processing at transmitting terminal.Multi-antenna receive diversity technology and transmit diversity techniques all utilize the multichannel space channel to realize the diversity processing.

   Characteristic

   The present invention proposes the OFDM single antenna reception diversity technology, it is characterized in that: only need adopt an antenna just can realize the diversity processing at receiving terminal.The OFDM single antenna reception diversity technology only utilizes one road space channel just can construct a plurality of channel frequency responses and realizes the diversity processing.The OFDM single antenna reception diversity technology can also be united use with existing transmit diversity techniques, also can use with existing multi-antenna receive diversity technical tie-up, further improves the performance of ofdm system.

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