Apparatus for OFDMA transmission and reception for coherent detection in uplink of wireless communication system and method thereof

• US 7,639,660 B2
• Filed: 09/14/2004
• Issued: 12/29/2009
• Est. Priority Date: 12/17/2003
• Status: Expired due to Fees

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Kim, Yun-Hee, Kim, Kwang-Soon, Ahn, Jae-Young
• Primary Examiner(s): Pérez-Gutiérrez; Rafael
• Assistant Examiner(s): Arevalo; Joseph
• Application Number:
  US10/941,197
• Publication Number:
  US 20050135324A1
• Time in Patent Office: 1,932 Days
• Field of Search: 370/345, 370/349, 370/344, 370/343, 370/204, 370/347, 370/503, 370/328, 370/329, 370/477, 370/236, 370/278, 370/436, 370/341, 370/331, 370/208, 370/310, 370/445, 370/252, 370/342, 370/441, 375/132, 375/347, 375/130, 375/260, 455/421, 455/548, 455/450, 455/503, 455/521, 455/452.1, 455/432.3, 455/433, 455/436, 455/434, 455/445
• US Class Current: 370/343
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 25/0224 using sounding signals
• CPC Class Codes: H04L 25/0236 using estimation of the other symbols
• CPC Class Codes: H04L 27/261 Details of reference signals
• CPC Class Codes: H04L 27/2626 Arrangements specific to the transmitter only
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

In the resource mapping method for data transmission, a time-frequency resource of a slot interval including OFDM symbols is divided into traffic channels and shared among the subscribers, the traffic channel including resource blocks uniformly distributed in the whole transmit frequency band, the resource block including consecutive subcarriers of consecutive received symbols having at least one inserted pilot symbol. The pilot symbols and the channel-encoded and modulated data symbols are processed by time-frequency mapping according to the resource-block-based mapping method to generate received symbols. The receiver separates the received symbols by subscribers according to the resource-block-based mapping method in a frequency domain, and performs iterative channel estimation, demodulation, and decoding by using the pilot and a data reference value after decoding for each traffic channel.

Claims

1. An apparatus for OFDMA (Orthogonal Frequency Division Multiple Access) transmission, which is for coherent detection in an uplink of a wireless communication system supporting multiple subscribers, the apparatus comprising:

a channel encoder for channel-encoding a subscriber data block;

a symbol mapper for mapping encoded data of the channel encoder into a data symbol;

a pilot symbol generator for generating a pilot symbol, the pilot symbol having the same transmission power as the data symbol;

a resource-block-based time-frequency mapper for mapping the data symbol output from the symbol mapper and the pilot symbol from the pilot symbol generator into a time-frequency index of an OFDM signal according to a resource-block-based mapping method, the resource-block-based mapping method mapping multiple resource blocks that are well-distributed in time and frequency domains to a channel allocated to a subscriber, each resource block comprising consecutive subcarriers of consecutive OFDM symbols and including at least one pilot symbol and multiple data symbols; and

an OFDM modulator for generating an OFDM signal from the mapped output of the resource-block-based time-frequency mapper,

wherein each resource block includes a single pilot symbol at the center of the resource block, the size of the resource block determined by R_fx R_t, where R_f and R_t satisfy the following expressions;

f_DT_sR_t <

<

½

, and τ

_maxΔ

f/R_f <

<

½

, where f_D is a maximum Doppler frequency of the channel, T_s is a symbol interval, and τ

_max is the maximum delay time of the channel, and Δ

f is the subcarrier spacing,

or each resource block includes multiple pilot symbols located at the same frequency and spaced in the time domain by a time spacing P determined by the following expression;

f_DT_sP<

1/2 .

2. The apparatus as claimed in claim 1, wherein the resource-block-based mapping method includes a single-pilot-based resource block mapping method or a multiple-pilot-based resource block mapping method.

3. An apparatus for OFDMA reception, which is for coherent detection in an uplink of a wireless communication system supporting multiple subscribers, the apparatus comprising:

an OFDM demodulator for converting OFDM received symbols at respective antennas into frequency-domain received symbols, the OFDM received symbol including a pilot symbol that has the same transmission power as a data symbol;

a resource-block-based time-frequency demapper for separating the frequency-domain received symbols of the OFDM demodulator by subscribers according to a resource mapping method for each subscriber, and rearranging the separated frequency-domain received symbols based on a resource block, the resource mapping method mapping multiple resource blocks that are well-distributed in time and frequency domains to each subscriber, each resource block comprising consecutive subcarriers of consecutive OFDM symbols;

a channel estimator for estimating a channel in units of resource blocks based on the output of the resource-block-based time-frequency demapper, wherein the channel estimator estimates, at a first iteration, the channel of a corresponding resource block based on a pilot channel estimate obtained by dividing the received pilot symbol output from the OFDM demodulator by a given pilot symbol and refines the estimated channel based on the pilot channel estimate and a data channel estimate in subsequent iterations;

a demodulator for coherently calculating a channel decoding input metric by using the channel estimate of the channel estimator; and

a channel decoder for performing channel decoding by using the calculated metric of the demodulator according to a channel encoding methods

wherein when using a single-pilot-based resource block having the pilot inserted in the center of the resource block, the channel estimator comprises;

an instantaneous pilot channel estimator for calculating an instantaneous pilot channel estimate;

a symbol mapper for estimating a transmit symbol from the output bit of the channel decoder;

an instantaneous data channel estimator for calculating an instantaneous data channel estimate by using the output of the symbol mapper;

a weighted sum calculator for transmitting the instantaneous pilot channel estimate as a channel value of the resource block in a first iteration, and calculating a weighted sum in the resource block according to a channel estimation method from the outputs of the instantaneous pilot channel estimator and the instantaneous data channel estimator in the subsequent iterations; and

a noise variance estimator for calculating the noise variance of the received symbols in the resource block.

4. The apparatus as claimed in claim 3, wherein the channel estimator estimates, at the first iteration, the channel of the corresponding resource block by using an instantaneous pilot channel estimate calculated by dividing the frequency-domain received pilot symbol output from the OFDM demodulator by the given pilot symbol, and estimates, in the subsequent iterations, the channel of the corresponding resource block by using both the instantaneous pilot channel estimate of the initial channel estimator in the resource block and the instantaneous data channel estimate calculated by using the decision symbols estimated from channel decoding decision bits.

5. The apparatus as claimed in claim 3, wherein the channel decoding input metric includes a Euclidean distance or a log-likelihood ratio.

6. The apparatus as claimed in claim 3, wherein the channel estimation method of the weighted sum calculator is selected from the group including an average channel estimation method, a weighted average channel estimation method, a modified average channel estimation method, and a modified weighted average channel estimation method.

7. The apparatus as claimed in claim 3, wherein when using a resource block having multiple inserted pilots, the channel estimator comprises:

an instantaneous pilot channel estimator for calculating an instantaneous pilot channel estimate;

a channel parameter estimator for estimating an SNR (signal-to-noise ratio) and a channel variation rate of a received packet using the instantaneous pilot channel estimates;

a filter coefficient memory and selector for selecting an initial filter coefficient matrix and a refining filter coefficient matrix with the outputs of the channel parameter estimator from the filter coefficient vector set calculated and stored in advance according to given levels of the SNR and the channel variation rate;

a reference symbol generator for estimating a transmit symbol from the decision bit of the channel decoder;

an instantaneous data channel estimator for generating an instantaneous data channel estimate from the output of the reference symbol generator;

a resource-block-based filter for performing a filtering operation in the units of resource block according to an initial filter coefficient matrix provided by the filter coefficient memory and selector; and

a noise variance estimator for calculating the noise variance of the received symbols in the resource block.

8. The apparatus as claimed in claim 7, wherein the resource-block-based filter filters, in the first iteration, the output of the instantaneous pilot channel estimator in the units of resource block according to the initial filter coefficient matrix provided by the filter coefficient memory and selector, and averages, in the subsequent iterations, the outputs of the instantaneous pilot channel estimator and the instantaneous data channel estimator corresponding to a same time in the resource block and filters the averaged outputs according to the refining filter coefficient matrix provided by the filter coefficient memory and selector.

9. A method for OFDMA transmission, which is for coherent detection in an uplink of a wireless communication system supporting multiple subscribers, the method comprising:

(a) channel-encoding a subscriber data block;

(b) mapping the encoded data into a data symbol;

(c) generating a pilot symbol, the pilot symbol having the same transmission power as the data symbol;

(d) mapping the symbol-mapped data symbol and the generated pilot symbol into a time-frequency index of an OFDM symbol according to a resource-block-based mapping method, the resource-block-based mapping method mapping multiple resource blocks that are well-distributed in time and frequency domains to a channel allocated to a subscriber, each resource block comprising consecutive subcarriers of consecutive OFDM symbols and including at least one pilot symbol and multiple data symbols; and

(e) generating an OFDM signal from the output of the time-frequency mapping step and transmitting the generated OFDM signal,

wherein each resource block includes a single pilot symbol at the center of the resource block, the size of the resource block determined by R_fx R_t, where R_f and R_t satisfy the following expressions;

f_DT_Rt <

<

1/2 , and τ

_maxΔ

f/R_f<

<

½

, where f_D is a maximum Doppler frequency of the channel. T_s is a symbol interval, and τ

_max is the maximum delay time of the channel, and Δ

f is the subcarrier spacing,

or each resource block includes multiple pilot symbols located at the same frequency and spaced in the time domain by a time spacing P determined by the following expression;

f_DT_sP<

½

.

10. A method for OFDMA reception, which is for coherent detection in an uplink of a wireless communication system supporting multiple subscribers, the method comprising:

(a) converting OFDM received symbols at respective antennas into frequency-domain received symbols by OFDM demodulation, the OFDM received symbol including a pilot symbol that has the same transmission power as a data symbol;

(b) separating the frequency-domain received symbols by subscribers according to a resource mapping method of each subscriber, and rearranging the separated frequency-domain received symbols based on a resource block by resource-block-based demapping, the resource mapping method mapping multiple resource blocks that are well-distributed in time and frequency domains to each subscriber, each resource block comprising consecutive subcarriers of consecutive OFDM symbols;

(c) estimating a channel in units of resource blocks by using the output of the time-frequency demapping, wherein the channel of a corresponding resource block is estimated, at a first iteration, based on a pilot channel obtained by dividing the received pilot symbol output from the OFDM demodulation by a given pilot symbol and is refined based on the pilot channel and a data channel estimate in subsequent iterations;

(d) coherently generating a channel decoding input metric from the received symbol, the estimated channel, and the estimated noise variance by demodulation;

(e) channel-decoding based on the generated metric according to a channel encoding method; and

(f) determining whether to repeat a reception process when a decoding stop condition provided in the channel decoding step is not satisfied, or when a iteration count is less than a maximum iteration counts

wherein when using a single-pilot-based resource block having the pilot inserted in the center of the resource block, estimating the channel in (c) comprises;

estimating an instantaneous pilot channel for calculating an instantaneous pilot channel estimate;

mapping a symbol for estimating a transmit symbol from the output bit of the channel decoder;

estimating an instantaneous data channel for calculating an instantaneous data channel estimate by using output of symbol mapping;

calculating a weighted sum for transmitting the instantaneous pilot channel estimate as a channel value of the resource block in a first iteration, and calculating a weighted sum in the resource block according to a channel estimation method from the instantaneous pilot channel estimate and the instantaneous data channel estimate in the subsequent iterations; and

estimating a noise variance for calculating the noise variance of the received symbols in the resource block.

11. The method as claimed in claim 10, wherein the step (c) comprises:

(c-1) performing an initial channel estimation in the first iteration to estimate the channel of the corresponding resource block by using an instantaneous pilot channel estimate calculated by dividing the frequency-domain received pilot symbol of the time-frequency demapping by the given pilot symbol, and to estimate a noise variance of a corresponding resource block by using given pilot symbols and tentatively decided data symbols from received symbols and channel estimates; and

(c-2) performing a refining channel estimation in the subsequent iterations to estimate the channel of the corresponding resource block by using both the instantaneous pilot channel estimate in the resource block and an instantaneous data channel estimate calculated by using a data modulation symbol estimated from channel decoded bits and to estimate the noise variance of the corresponding resource block by using pilot symbols and data symbols estimated from channel decoded bits.

12. The method as claimed in claim 11, wherein when the received symbol has a resource block comprising multiple consecutive time-frequency resources almost without a variation of channel and has a single-pilot-based resource block having a pilot symbol inserted in the center of the resource block

the step (c-1) includes using the single instantaneous pilot channel estimate in the resource block as a data channel estimate in the resource block, and

the step (c-2) includes estimating the data channel by using a weighted sum of the instantaneous pilot channel estimate and the instantaneous data channel estimate.

13. The method as claimed in claim 12, wherein the step (c-2) includes estimating the data channel by an average channel estimation method of averaging all instantaneous channel estimates in the resource block, for the weighted sum.

14. The method as claimed in claim 12, wherein the step (c-2) includes estimating the data channel by a modified average channel estimation method of averaging all instantaneous channel estimates other than the instantaneous channel estimate of the data channel to be estimated, for the weighted sum.

15. The method as claimed in claim 12, wherein the step (c-2) includes estimating the data channel by a weighted average channel estimation method of calculating the APP of a modulation symbol estimated from the APPs of the decision bits of the channel decoding step (e), adding the APP of a modulation symbol as an extra weight to the instantaneous channel estimate in the resource block, and averaging the weighted instantaneous channel estimate, for the weighted sum.

16. The method as claimed in claim 12, wherein the step (c-2) includes using a modified weighted average channel estimation method of averaging the instantaneous channel estimate other than a value of a data position to be estimated, in calculating the APP of a symbol estimated from the APPs of decision bits of the channel decoding step (e), adding the APP as an extra weight to the instantaneous channel estimate in the resource block, and averaging the weighted instantaneous channel estimate, for the weighted sum.

17. The method as claimed in claim 11, wherein when the received symbol has a resource block comprising consecutive time-frequency resources allowing a variation of channel in a time domain almost without a variation of channel in a frequency axis and is mapped into a multiple-pilot-based resource block having at least two inserted pilot symbols,

the step (c-1) includes filtering the instantaneous pilot channel estimate to estimate a data channel, and

the step (c-2) includes dividing a data channel received symbol by a modulation symbol estimated from the channel decoded bits to calculate an instantaneous data channel estimate, averaging instantaneous channel estimates for different frequency indices of a same time index in the resource block in a frequency axis, and filtering the average value in the time domain to estimate the channel.

18. The method as claimed in claim 17, wherein the steps (c-1) and (c-2) include determining an initial filter coefficient matrix set and a refining filter coefficient matrix set, respectively, according to the ranges of the SNR and the channel variation rate, selecting an initial filter coefficient vector and a refining filter coefficient matrix for the received data packet according to the estimates of the SNR and the channel variation rate, and performing a filtering operation.

19. The method as claimed in claim 18, wherein the steps (c-1) and (c-2) include estimating the channel parameters including the SNR and the channel variation rate by using the instantaneous pilot channel estimates in a received data packet.

20. A method for OFDMA transmission and reception, which is for coherent detection in an uplink of a wireless communication system supporting multiple subscribers, the method comprising:

a transmission process comprising (a) dividing time-frequency resources of a time slot comprising a plurality of orthogonal frequency division multiplexing symbols into a plurality of traffic channels, each traffic channel comprising a plurality of resource blocks that are well-distributed in time and frequency domains of the time slot, (b) generating pilot symbols according to a resource-block-based resource mapping method with a minimum resource unit being one of the resource blocks, each resource block comprising consecutive subcarriers of consecutive OFDM symbols having at least one inserted pilot symbol for each traffic channel, and (c) processing the pilot symbols and channel-encoded and modulated data symbols by time-frequency mapping according to the resource-block-based mapping method to generate and transmit an OFDM signal, wherein each resource block includes a single pilot symbol at the center of the resource block, the size of the resource block determined by R_fx R_t, where R_f and R_t satisfy the following expressions;

f_DT_sR_t <

<

½

, and τ

_maxΔ

f / R_f ½

, where f_D is a maximum Doppler frequency of the channel, T_s is a symbol interval, and τ

_max is the maximum delay time of the channel, and Δ

f is the subcarrier spacing,

or each resource block includes multiple pilot symbols located at the same frequency and spaced in the time domain by a time spacing P determined by the following expression;

f_DT_sP<

½

;

and

a reception process comprising (d) processing the received OFDM signal according to the resource-block-based mapping method in the frequency domain, separating the received symbols by subscribers, and rearranging the separated symbols based on the resource block, and (e) performing iterative channel estimation, demodulation, and decoding by using the pilot symbols and data symbols estimated with the channel decoded bits after decoding for each traffic channel, wherein the traffic channel of a corresponding resource block is estimated, at a first iteration, based on a pilot channel estimate obtained by dividing the received pilot symbol output from the demodulation by a given pilot symbol and is refined based on the pilot channel and a data channel estimate in subsequent iterations.