Frequency domain equalization for single-carrier broadband wireless systems

doi:10.1109/35.995852

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Frequency domain equalization for single-carrier broadband wireless systems

Journal Article•DOI•

Frequency domain equalization for single-carrier broadband wireless systems

David Falconer¹, S.L. Ariyavisitakul, A. Benyamin-Seeyar², B. Eidson³•Institutions (3)

Carleton University¹, Harris Corporation², Conexant³

01 Apr 2002-IEEE Communications Magazine (IEEE)-Vol. 40, Iss: 4, pp 58-66

TL;DR: This article surveys frequency domain equalization (FDE) applied to single-carrier (SC) modulation solutions and discusses similarities and differences of SC and OFDM systems and coexistence possibilities, and presents examples of SC-FDE performance capabilities.

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Abstract: Broadband wireless access systems deployed in residential and business environments are likely to face hostile radio propagation environments, with multipath delay spread extending over tens or hundreds of bit intervals. Orthogonal frequency-division multiplex (OFDM) is a recognized multicarrier solution to combat the effects of such multipath conditions. This article surveys frequency domain equalization (FDE) applied to single-carrier (SC) modulation solutions. SC radio modems with frequency domain equalization have similar performance, efficiency, and low signal processing complexity advantages as OFDM, and in addition are less sensitive than OFDM to RF impairments such as power amplifier nonlinearities. We discuss similarities and differences of SC and OFDM systems and coexistence possibilities, and present examples of SC-FDE performance capabilities.

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Journal Article•

DS-CDMA Frequency-domain Multi-access Interference Canceller

[...]

Ishihara Koichi, Takeda Kazuaki, Adachi Fumiyuki

21 Jan 2005-IEICE technical report. Communication systems

TL;DR: FDE: frequency-domain equalization, MAI: Inter-path interference, BER: multi-access interference, more details to come.

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Abstract: あらまし Rake 合成を用いる DS-CDMA では,チャネルの周波数選択性が厳しくなるとパス間干渉が無視できなくなり誤り率特性が劣化してしまうことが知られている.最近,周波数領域等化(FDE: frequency-domain equalization)技術を適用することで大幅に誤り率特性を改善できることが分かってきた.しかし,複数ユーザが基地局にアクセスする上りリンクでは,たとえ FDE を用いてもパス間干渉(IPI: Inter-path interference)により大きなMAI(multi-access interference)が発生し,ビット誤り率(BER)特性が劣化してしまう.また,基地局から各ユーザにアクセスする下りリンクにおいても,ユーザ間の直交性が保たれず BER 特性が劣化してしまうことが知られている.そこで本論文では,DS-CDMA上り/下りリンクを対象に MAIを軽減する周波数領域干渉キャンセラを提案し,誤り率特性の改善効果を計算機シミュレーションによって明らかにしている.また送受信アンテナダイバーシチを併用したときの効果についても明らかにしている. キーワード DS-CDMA,周波数領域等化,MAI,IPI,キャンセラ,送受信アンテナダイバーシチ

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4 citations

Additional excerpts

...計算機シミュレーション計算機シミュレーション諸元を表 1 に示す．QPSK データ変調，FFT ポイント数 Nc=256（フレーム長 256 チップ）およびガードインターバル Ng=32 とした．またフェージングチャネルは，16 パス (L=16)の一様電力遅延プロファイル ( LhEhE lmn u lmn /1]|[|]|[| 2 ,, 2 ,, == )を有する周波数選択性のブロックレイリーフェージングチャネルであるものとする．なお，受信機のタイミング再生とチャネル推定は理想的であり，全ユーザの送信信号が GI 内に収まるよう送信タイミングコントロールができているものとした．表 1 計算機シミュレーション諸元 Modulat ion QPSK Number of FFT points Nc=256 GI length Ng=32 Spreading sequence Long PN sequence Spreading Factor SF=16 Transmitter Number of user U=16 Fading Frequency-select ive Block Rayleigh fading Number of paths L=16 path Channel Power delay profile Uniform Receiver Frequency-domain Equalizat ion MMSE 図 5にユーザ数 U=16(全多重 )のときのステージ毎の平均 BER 特性を示す．図 5(a)は STBC と受信アンテナダイバーシチを用いない場合 (NBS=NMS=1)であり，図 5(b)は上り /下りリンク共に NBS=NMS=2 の場合である．横軸は 1 ビットあたりの受信信号エネルギー対雑音電力スペクトル密度 Eb/N0 であり， Eb/N0=SF(1+Ng/Nc)(Ec/N0)の関係にある．比較のため， MAI が完全に除去できたときの特性 (U=1)も示す．上りリンクでは，送信タイミングが非同期であることと各ユーザでフェージングが異なるため大きな MAI が生じるため誤りフロアが見られる．しかしながら，周波数領域 MAI キャンセラを用いることによって MAI を軽減することができ，BER 特性が改善できることが分かる．一方，下りリンクでは各ユーザの送信タイミングは同期し，チャネルが全ユーザで同一なため，誤りフロアは見られないが，周波数領域等化を用いても完全にはチャネルは周波数非選択性に復元できないため，MAI が発生し，特性が劣化している．しかしながら，周波数領域 MAI キャンセラを用いることで特性が改善している．NBS=NMS=1 の場合，上り (下り )リンクでは i=6(3)程度のステージ数でシングルユーザ時 (U=1)に近い BER 特性が得られている．また， NBS=NMS=2 の場合，送受信アンテナダイバーシチ効果により，BER 特性が大幅に改善し，ステージ数も上り (下り )リンクでは i=3(2)程度でシングルユーザ時に近い BER 特性が得られている． 5....
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...最近,シングルキャリア伝送に周波数領域等化を用いると周波数ダイバーシチ効果を積極的に利用でき, BER 特性を改善できることが示された [7]....
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...まえがき次世代移動通信システムでは，高速かつ高品質のデータ伝送が要求される．しかし，伝搬路が遅延の異なる複数のパスで構成されるために周波数選択性フェージングが発生し，シングルキャリア伝送では伝送特性が大幅に劣化してしまう [1]．直接拡散符号分割マルチアクセス (DS-CDMA)では，複数のパスを分離し，Rake 受信を行うことにより，パスダイバーシチ効果を得て，ビット誤り率 (BER)特性を改善することができる．そこで第 3 世代携帯電話では，広帯域 DS-CDMA が用いられている [2]．次世代移動通信システムでは 100Mbps を超える伝送速度が必要であると言われている．このような高速伝送では，分解可能なパス数が増加してしまうことでパス間干渉が増大するため，Rake 受信を用いても BER 特性が大幅に劣化してしまう．そこで最近では，直交周波数分割多重 (OFDM)やマルチキャリア符号分割マルチアクセス (MC-CDMA)といった，多数の直交サブキャリアを用いて並列伝送するマルチキャリア伝送が注目されている [3-6]．MC-CDMA では，Rake 受信を用いる DS-CDMAよりも優れた BER特性が得られる．しかし，マルチキャリア伝送では送信信号のピーク対平均信号電力比 (PAPR)がサブキャリア数に比例して大きくなるため，線形送信電力増幅器の負担が増大してしまうという課題がある．最近，シングルキャリア伝送に周波数領域等化を用いると周波数ダイバーシチ効果を積極的に利用でき， BER 特性を改善できることが示された [7]．筆者らは， Rake受信の代わりに周波数領域等化を DS-CDMAに適用すれば BER 特性を大幅に改善でき，MC-CDMA と等価な BER 特性を得ることができることを示した [8,9]．周波数領域等化を用いる DS-CDMA の利点は， MC-CDMA と比較してピーク対平均信号電力比 (PAPR) の問題が少ないこと，等化器の複雑性が周波数選択性の強さに依存しないことなどが挙げられる．しかし，複数のユーザが基地局にアクセスする上りリンクの場合，送信タイミングが各ユーザで非同期であること，そして各ユーザでフェージングチャネルが異なることから大きなマルチアクセス干渉 (MAI)が発生し，BER 特性が大幅に劣化してしまう [10-13]．また，基地局から各ユーザにアクセスする下りリンクの場合，パス間干渉 (IPI)の影響でユーザ間の直交性が保たれず大きな MAI がやはり発生し，BER 特性が劣化してしまう [9,10]．本論文では， DS-CDMA 上り /下りリンクにおける周波数領域 MAI キャンセラを提案する．また，BER 特性改善に効果的な時空間ブロック符号化 (STBC)を用いた送信ダイバーシチ [10,14]および受信アンテナダイバーシチの併用したときの BER 特性改善について検討する．本論文の構成は以下のようになっている．第 2 章では周波数領域等化を用いた DS-CDMA 上り / 下りリンク伝送系について述べ，第 3 章では，提案する周波数領域 MAI キャンセラの構成について述べる．第 4 章では，周波数選択性レイリーフェージングチャネルにおける平均 BER 特性を計算機シミュレーションで求めている．第 5 章はむすびである． 2....
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...+M M SE IF FT C hi p de - in te rle av er IF FT (b) 第 i ステージ ( 2≥i ) )( ~ 1 nd Ui − Te nt at iv e de ci si on C hi p in te rle av er FF T )(0 tc )(tpn )( ~0 ndi STBC )(0),1or(0 kH#0 #1 ・・・ #U-1 #0 ・・・ )(~0 ,0),or( kR ioe )(~ 1 ,1),or( kR U ioe − Nc ・・・ Te nt at iv e de ci si on C hi p in te rle av er FF T (c) レプリカ生成部図 4 下りリンク周波数領域 PIC の第 i 番目のステージのキャンセル処理 10-5 10-4 10-3 10-2 10-1 100 0 5 10 15 20 i=1 2 3 4 5 6 7 1 2 3 4 Perfect (U=1) A ve ra ge B ER Average received E b /N 0 per receive antenna (dB) Uplink Downlink SF=16 N BS =N MS =1 U=16 (a) No diversity (Nt=Nr=1) 10-5 10-4 10-3 10-2 10-1 100 0 5 10 15 20 i=1 2 3 4 1 2 3 Perfect (U=1) A ve ra ge B ER Average received E b /N 0 per receive antenna (dB) UL DL SF=16 N BS =N MS =2 U=16 (b) Nt=Nr=2 図 5 周波数領域 MAI キャンセラの平均 BER 特性...
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...むすび DS-CDMA上り /下りリンクにおける周波数領域 MAI キャンセラを提案した．上りリンクでは逐次的に干渉を軽減するマルチステージ SIC を，下りリンクでは処理遅延の少ないマルチステージ PIC を用いることで，平均 BER 特性が大幅に改善できることを計算機シミュレーションによって明らかにした．また，送受信アンテナダイバーシチを併用することで，平均 BER 特性が更に改善されることを示した．本論文で得られた結果をまとめると以下のようになる．・ NBS=NMS=1 の場合，上り (下り )リンクでは i=6(3)ステージ目でシングルユーザ時に近い BER 特性が得られる．・送受信アンテナダイバーシチを併用することで BER 特性が更に改善されるので，MAI キャンセラのステージ数も上り (下り )リンク i=3(2)程度と少なく済む．文献 [1] W.C., Jakes Jr. , Ed., Microwave mobile communications , Wiley, New York, 1974....
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Single Carrier Modulation With Nonlinear Frequency Domain Equalization: An Idea Whose Time Has ComeVAgain In high-speed single-carrier digital communication systems, processing blocks of signals using Fast Fourier Transforms is an efficient way to equalize (compensate) for interference between transmitted symbols.

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Nevio Benvenuto, Rui Dinis, David Falconer, Stefano Tomasin

01 Jan 2010

TL;DR: This tutorial paper aims at providing an overview of nonlinear equalization methods as a key ingredient in receivers of SCM for wideband transmission, reviewing both hybrid (with filters implemented both in time and frequency domain) and all-frequency-domain iterative struc- tures.

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Abstract: Inrecentyearssinglecarriermodulation(SCM)has again become an interesting and complementary alternative to multicarriermodulations suchas orthogonalfrequencydivision multiplexing (OFDM). This has been largely due to the use of nonlinear equalizer structures implemented in part in the frequency domain by means of fast Fourier transforms, bringing the complexity close to that of OFDM. Here a nonlinear equalizer is formed with a linear filter to remove part of intersymbol interference, followed by a canceler of remaining interference by using previous detected data. Moreover, the capacity of SCM is similar to that of OFDM in highly dispersive channels only if anonlinear equalizeris adoptedat the receiver. Indeed, the study of efficient nonlinear frequency domain equalization techniques has further pushed the adoption of SCM in various standards. This tutorial paper aims at providing an overview of nonlinear equalization methods as a key ingredient in receivers of SCM for wideband transmission. We review both hybrid (with filters implemented both in time and frequency domain) and all-frequency-domain iterative struc- tures. Application of nonlinear frequency domain equalizers to a multiple input multiple output scenario is also investigated, with a comparison of two architectures for interference reduction. We also present methods for channel estimation and alternatives for pilot insertion. The impact on SCM transmission of impairments such as phase noise, frequency offset and saturation due to high power amplifiers is also assessed. The comparison among the considered frequency domain equalization techniques is based both on complexity and performance, in terms of bit error rate or throughput.

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4 citations

Cites methods or result from "Frequency domain equalization for s..."

...In the hybrid DFE (HDFE), the feedforward filter operates in the FD on blocks of the received signal, while thefeedbackoperatesintheTD[16],[ 38 ].Inordertoallow TD implementation of the feedback filter, data transmission with a PN extension [see (11)] must be considered instead of cyclic prefix....
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...When SCM with frequency domain equalization is aided by FD nonlinear equalizers, its BER performance improves markedly, and it can come very close to the performance of comparable OFDM systems [16], [ 38 ]....
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Journal Article•DOI•

Systematic design of single carrier overlap frequency domain equalization

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Wladimir Bocquet¹, Kazunori Hayashi², Hideaki Sakai²•Institutions (2)

Orange S.A.¹, Kyoto University²

25 Feb 2010-Journal of Systems Science & Complexity

TL;DR: Simulation results show that the proposed scheme can achieve comparable BER performance to the conventional SC-FDE scheme with sufficient GI insertion for both the coded and uncoded cases with various modulation levels, while requiring lower computational complexity compared to the SC overlap FDE transmission with the fixed block.

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Abstract: This paper proposes a systematic design method of overlap frequency domain equalization (FDE) for single carrier (SC) transmission without a guard interval (GI). Based on the analysis of signal-to-interference-plus-noise ratio (SINR) of the equalizer output for each symbol, the authors adaptively determine the block of the overlap FDE, where the block is defined as a set of symbols at the equalizer output with sufficiently low error rate, for a certain fixed sliding window size, which corresponds to a fast Fourier transform (FFT) window size. The proposed method takes advantage of the fact that the utility part of the equalized signal is localized around the center of the FFT window. In addition, the authors also propose to adjust the block size in order to control the computational complexity of the equalization per processed sample associating with the average bit error rate (BER) of the system. Simulation results show that the proposed scheme can achieve comparable BER performance to the conventional SC-FDE scheme with sufficient GI insertion for both the coded and uncoded cases with various modulation levels, while requiring lower computational complexity compared to the SC overlap FDE transmission with the fixed block.

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4 citations

Cites methods from "Frequency domain equalization for s..."

...In addition, we also propose to adjust the block size in order to control the computational complexity of the equalization per processed sample associating with the average bit error rate (BER) of the system....
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Proceedings Article•DOI•

The role of virtual noise in unconstrained frequency domain equalization

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Maurizio Magarini¹, Arnaldo Spalvieri¹•Institutions (1)

Polytechnic University of Milan¹

05 Sep 2004

TL;DR: This paper considers the minimum mean square error (MMSE) DFE with feedforward filter in the discrete frequency domain, and finds that the error rate can be significantly improved by deliberately augmenting the power of the noise in the computation of the transfer function of the frequency domain feedforwardfilter.

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Abstract: Decision feedback equalization is a popular method for signal detection that allows a good trade off between complexity and performance. The complexity of the decision feedback equalizer (DFE) is mainly concentrated in the feedforward filter, which is often realized in FIR form. When the number of taps of the FIR filter needed to obtain nearly optimal performance becomes large, one may take advantage of the efficiency of the FFT/IFFT algorithm realizing the feedforward filter in the discrete frequency domain. In this paper we consider the minimum mean square error (MMSE) DFE with feedforward filter in the discrete frequency domain, assuming perfect knowledge of a static channel. We move from the observation that the optimal MMSE-DFE feedforward filter is IIR, and point out that the classical scheme of unconstrained frequency domain filtering with overlap/save digital signal processing may induce substantial increase in the error rate when the approximation of the linear convolution between the received signal and the mentioned IIR, to a circular convolution is poor. Our main finding is that the error rate can be significantly improved by deliberately augmenting the power of the noise in the computation of the transfer function of the frequency domain feedforward filter.

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4 citations

Proceedings Article•DOI•

Performance comparison of cooperative OFDM and SC-FDE relay networks in a frequency-selective fading channel

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Alina Alexandra Florea¹, Haris Gacanin², Fumiyuki Adachi²•Institutions (2)

Institut national des sciences Appliquées de Lyon¹, Tohoku University²

01 Nov 2010

TL;DR: A performance comparison of cooperative OFDM relay network and cooperative SC-FDE relay network with pilot-assisted channel estimation is presented and a joint diversity combining and FDE is considered in order to obtain a larger frequency diversity gain.

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Abstract: Cooperative networking schemes provide spatial diversity gain (named cooperative diversity gain) using the antennas of spatially distributed users. Consistent research has been focusing on cooperative networks using orthogonal frequency division multiplexing (OFDM) and single carrier with frequency domain-equalization (SC-FDE). Coherent detection and frequency-domain equalization (FDE) require accurate channel estimation. In this paper, we present a performance comparison of cooperative OFDM relay network and cooperative SC-FDE relay network with pilot-assisted channel estimation. We consider a joint diversity combining and FDE in order to obtain a larger frequency diversity gain. When channel coding is used, cooperative OFDM relay network performs similarly to cooperative SC-FDE relay network in a frequency-selective fading channel.

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4 citations

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References

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More filters

Book•

Adaptive Filter Theory

[...]

Simon Haykin

01 Jan 1986

TL;DR: In this paper, the authors propose a recursive least square adaptive filter (RLF) based on the Kalman filter, which is used as the unifying base for RLS Filters.

...read moreread less

Abstract: Background and Overview. 1. Stochastic Processes and Models. 2. Wiener Filters. 3. Linear Prediction. 4. Method of Steepest Descent. 5. Least-Mean-Square Adaptive Filters. 6. Normalized Least-Mean-Square Adaptive Filters. 7. Transform-Domain and Sub-Band Adaptive Filters. 8. Method of Least Squares. 9. Recursive Least-Square Adaptive Filters. 10. Kalman Filters as the Unifying Bases for RLS Filters. 11. Square-Root Adaptive Filters. 12. Order-Recursive Adaptive Filters. 13. Finite-Precision Effects. 14. Tracking of Time-Varying Systems. 15. Adaptive Filters Using Infinite-Duration Impulse Response Structures. 16. Blind Deconvolution. 17. Back-Propagation Learning. Epilogue. Appendix A. Complex Variables. Appendix B. Differentiation with Respect to a Vector. Appendix C. Method of Lagrange Multipliers. Appendix D. Estimation Theory. Appendix E. Eigenanalysis. Appendix F. Rotations and Reflections. Appendix G. Complex Wishart Distribution. Glossary. Abbreviations. Principal Symbols. Bibliography. Index.

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16,062 citations

"Frequency domain equalization for s..." refers methods in this paper

...Adaptation can be done with LMS (least mean square), RLS, or least squares minimization (LS) techniques, analogous to adaptation of time domain equalizers [Hay96], [Cla98]....
[...]
...Overlap-save or overlap-add signal processing techniques could also be used to avoid the extra overhead of the cyclic prefix [Fer85], [Hay96]....
[...]

Journal Article•DOI•

Analysis and Simulation of a Digital Mobile Channel Using Orthogonal Frequency Division Multiplexing

[...]

Jr. L.J. Cimini¹•Institutions (1)

Bell Labs¹

01 Jul 1985-IEEE Transactions on Communications

TL;DR: The analysis and simulation of a technique for combating the effects of multipath propagation and cochannel interference on a narrow-band digital mobile channel using the discrete Fourier transform to orthogonally frequency multiplex many narrow subchannels, each signaling at a very low rate, into one high-rate channel is discussed.

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Abstract: This paper discusses the analysis and simulation of a technique for combating the effects of multipath propagation and cochannel interference on a narrow-band digital mobile channel. This system uses the discrete Fourier transform to orthogonally frequency multiplex many narrow subchannels, each signaling at a very low rate, into one high-rate channel. When this technique is used with pilot-based correction, the effects of flat Rayleigh fading can be reduced significantly. An improvement in signal-to-interference ratio of 6 dB can be obtained over the bursty Rayleigh channel. In addition, with each subchannel signaling at a low rate, this technique can provide added protection against delay spread. To enhance the behavior of the technique in a heavily frequency-selective environment, interpolated pilots are used. A frequency offset reference scheme is employed for the pilots to improve protection against cochannel interference.

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2,627 citations

"Frequency domain equalization for s..." refers background in this paper

...OFDM transmits multiple modulated subcarriers in parallel [ 1 ]....
[...]
...Several variations of orthogonal frequency-division multiplexing (OFDM) have been proposed as effective anti-multipath techniques, primarily because of the favorable trade-off they offer between performance in severe multipath and signal processing complexity [ 1 ]....
[...]

Book•

Adaptive filter theory (2nd ed.)

[...]

Simon Haykin¹•Institutions (1)

McMaster University¹

01 Mar 1991

2,447 citations

Journal Article•DOI•

BER sensitivity of OFDM systems to carrier frequency offset and Wiener phase noise

[...]

Thierry Pollet¹, M. Van Bladel¹, Marc Moeneclaey¹•Institutions (1)

Ghent University¹

01 Feb 1995-IEEE Transactions on Communications

TL;DR: In this contribution the transmission of M-PSK and M-QAM modulated orthogonal frequency division multiplexed (OFDM) signals over an additive white Gaussian noise (AWGN) channel is considered and the degradation of the bit error rate is evaluated.

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Abstract: In this contribution the transmission of M-PSK and M-QAM modulated orthogonal frequency division multiplexed (OFDM) signals over an additive white Gaussian noise (AWGN) channel is considered. The degradation of the bit error rate (BER), caused by the presence of carrier frequency offset and carrier phase noise is analytically evaluated. It is shown that for a given BER degradation, the values of the frequency offset and the linewidth of the carrier generator that are allowed for OFDM are orders of magnitude smaller than for single carrier systems carrying the same bit rate. >

...read moreread less

1,816 citations

Journal Article•DOI•

Polyphase codes with good periodic correlation properties (Corresp.)

[...]

D. Chu¹•Institutions (1)

Hewlett-Packard¹

01 Jul 1972-IEEE Transactions on Information Theory

TL;DR: This correspondence describes the construction of complex codes of the form exp i \alpha_k whose discrete circular autocorrelations are zero for all nonzero lags.

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Abstract: This correspondence describes the construction of complex codes of the form exp i \alpha_k whose discrete circular autocorrelations are zero for all nonzero lags. There is no restriction on code lengths.

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1,624 citations