Frequency domain equalization for single-carrier broadband wireless systems
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.
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.
Citations
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01 Nov 2011
TL;DR: It is shown that the performance of grouped allocation and interleaved allocation becomes similar in the presence of CFOs as opposed to the perfect synchronization scenario, and the performance degradation due to CFO is relatively small for SC-FDMA with zero forcing equalization.
Abstract: Single carrier frequency division multiple access (SC-FDMA) has been adopted for multi-user systems due to its low peak to average power ratio and improved bit error rate performance as compared to orthogonal frequency division multiple access (OFDMA) with minimum mean square error (MMSE) equalization. In this paper, we investigate the robustness of these two technologies in the presence of carrier frequency offsets (CFOs) for uplink transmissions. We present a generalized system model for SC-FDMA and OFDMA uplink transmissions and compare the bit error rate performance of different sub-carrier allocation and CFO compensation schemes. We show that surprisingly, SC-FDMA is more sensitive to CFOs as compared to OFDMA, so the performance gains offered by SC-FDMA with MMSE equalization are lost in the presence of CFOs. On the other hand, the performance degradation due to CFO is relatively small for SC-FDMA with zero forcing equalization. We also show that the performance of grouped allocation and interleaved allocation becomes similar in the presence of CFOs as opposed to the perfect synchronization scenario.
3 citations
Cites result from "Frequency domain equalization for s..."
...As DR(hm0) is a diagonal matrix, per sub-carrier FDE can be performed to recover the transmitted signal xm0(q) as, x̂m0(q) = HHm0Hm0 1 HHm0Ym0(q), (12) for ZF equalization and, x̂m0(q) = HHm0 ✓ HHm0Hm0 + 2w 2x IR ◆ 1 Ym0(q), (13) for MMSE equalization, where 2x is the average power of the transmitted signal....
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...This fact enables low complexity frequency domain equalization (FDE) [8] in SC-FDMA, similar to OFDMA....
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09 Jul 2006
TL;DR: It is shown that one can do away with the cyclic prefix (CP) for SC-FDE and OFDM at the cost of a moderate increase in complexity of a DFT-based receiver.
Abstract: We show that one can do away with the cyclic prefix (CP) for SC-FDE and OFDM at the cost of a moderate increase in complexity of a DFT-based receiver. Such an approach effectively deals with the decrease in the number of channel uses due to the introduction of the CP. It is shown that the SINR for SC-FDE remains the same asymptotically with the proposed receiver without CP as that of the conventional receiver with CP.
3 citations
04 Dec 2007
TL;DR: Simulation results show that the proposed receiver scheme can achieve better bit error rate (BER) performance than MMSE-FDE and FDE-PIC, which is a combination of MMSE and multistage PIC.
Abstract: In this paper, we propose a hybrid receiver scheme called FDE-PPIC, which combines minimum-mean-square-error frequency domain equalization (MMSE-FDE) with multistage partial parallel interference cancellation (P-PIC), for the downlink of single-carrier cyclic-prefix code division multiple access (CP-CDMA) system over frequency-selective channels. MMSE-FDE instead of conventional RAKE receiver is utilized to alleviate the effect of frequency- selective channel and obtain the initial data estimation. Multistage P-PIC in frequency domain is then employed to mitigate the residual multiuser interference (MUI) for further improving the system performance. Simulation results show that the proposed receiver scheme can achieve better bit error rate (BER) performance than MMSE-FDE and FDE-PIC which is a combination of MMSE-FDE and multistage PIC.
3 citations
Cites background from "Frequency domain equalization for s..."
...Recently, much attention has been focused on another broadband wireless communication system, namely cyclic-prefix code division multiple access (CP-CDMA), which combines the CP concept of OFDM with single-carrier DS-CDMA to enable efficient frequency domain equalization (FDE) over severe frequency-selective fading channels [3, 4]....
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TL;DR: A method to exploit the redundancy of the padding to recover this lost information, leading to two new frequency-domain equalizers, a ZFE and an MMSE-like equalizer, which have a performance close to the time-domainequalizers, while maintaining the low complexity of the original frequency- domain equalizers.
Abstract: This paper focuses on the equalization of block transmissions with zero pad (ZP). If the channel impulse response length does not exceed the ZP length, it is possible to construct zero-forcing equalizers (ZFEs). Improved performance may be achieved using a minimum mean squared error (MMSE) equalizer. However, these equalizers are computationally intensive when a time-domain implementation is used. While the frequency-domain implementation of a ZFE has a lower complexity, it is prone to—potentially infinite—noise enhancement in the presence of spectral zeros. The MMSE equalizer in the frequency domain performs better by limiting the noise enhancement but still loses all information stored at the spectral zeros. This paper presents a method to exploit the redundancy of the padding to recover this lost information, leading to two new frequency-domain equalizers, a ZFE and an MMSE-like equalizer. These two equalizers are evaluated through simulations. They have a performance close to the time-domain equalizers, while maintaining the low complexity of the original frequency-domain equalizers. The equalizers are especially useful for scenarios with a high signal-to-noise ratio (SNR), where the performance is not limited by the presence of noise, but by the absence of the information stored in the spectral zeros. In practice, this means an SNR >30 dB. With minor modifications, the equalizers can also be applied if the ZP is replaced by a unique word (UW).
3 citations
Cites background or methods from "Frequency domain equalization for s..."
...The differences mostly concern practical implementation issues: because SC systems generally have a lower peak-to-average power ratio (PAPR) and a better robustness against non-linearities or carrier offset [6, 8, 9], their demands on the analog hardware are lower than those of OFDM....
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...A CP-OFDM system can take this into account by discarding the affected sub-carriers if the channel is known at the transmitter or by using forward error correction (FEC) codes if it is not [8, 11]....
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Patent•
26 May 2016
TL;DR: In this article, a hybrid band intelligent backhaul radio (HB-IBR) is proposed, which is a combination of two radios operating in different bands, such that a common medium access control (MAC) block may be utilized between the dual radios.
Abstract: A hybrid band intelligent backhaul radio (HB-IBR) is disclosed that is a combination of two radios operating in different bands. Embodiments include a dual radio configuration wherein a first radio operates in a non-line of sight (NLOS) radio link configuration and a second ancillary radio operates in a near line of sight or line of sight configuration (n)LOS. For example, the HB-IBR may have an Intelligent Backhaul Radio (IBR) operating in the non-line of sight mode of operation within the 5.8 GHz unlicensed band, and have an ancillary radio link operating in the FCC part 101 E band of operation at 60 GHz. A common medium access control (MAC) block may be utilized between the dual radios.
3 citations
References
More filters
Book•
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.
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.
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]....
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...Overlap-save or overlap-add signal processing techniques could also be used to avoid the extra overhead of the cyclic prefix [Fer85], [Hay96]....
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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.
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.
2,627 citations
"Frequency domain equalization for s..." refers background in this paper
...OFDM transmits multiple modulated subcarriers in parallel [ 1 ]....
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...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 ]....
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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.
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. >
1,816 citations
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.
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.
1,624 citations