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
More filters
09 Jul 2019
TL;DR: It is shown that the demand for flicker-free lighting can easily be met with line codes, and together with an equalization, the AC coupling at the receiver is no problem either.
Abstract: Lighting requirements and their impact on visible light communication (VLC) systems based on multi-level pulse-amplitude modulation are discussed. We will show that the moving average of the signal must not fluctuate too much. Two solutions are presented. One is based on a simple extension of the well-known 5B6B line coding to codes with M-ary symbols. The other is based on the so-called Hadamard-coded modulation. Closely related to the topic of DC balance is the resistance of the received signal to high-pass filtering. The impact of such filtering on multi-level PAM systems with frequency domain equalization is investigated. We will show that the demand for flicker-free lighting can easily be met with line codes. Together with an equalization, which has to be used for multi-level PAM anyway, the AC coupling at the receiver is no problem either. The feasibility of an adaptive modulation is also discussed.
6 citations
Cites background from "Frequency domain equalization for s..."
...An important assumption for the evaluation of the bit error rate (BER) will therefore be that the transmission is combined with a zero-forcing frequency domain equalization [3, 6]....
[...]
TL;DR: This paper develops an expectation maximization (EM) based approach to separately estimate TX and RX I/Q imbalances, and the multipath channel, and shows that the proposed scheme outperforms the counterparts, and can significantly mitigate the adverse effects of I/Z imbalance.
Abstract: Due to the non-ideality of analog components, transmitters (TXs) and receivers (RXs) suffer from hardware impairments such as in-phase/quadrature (I/Q) imbalance, which manifests itself as the mismatches of amplitude, phase and frequency response between I/Q branches. Without compensation, I/Q imbalance can severely degrade the system performance. This paper addresses the joint compensation of TX and RX I/Q imbalances for single carrier frequency domain equalization (SC-FDE) systems. Specifically, we develop an expectation maximization (EM) based approach to separately estimate TX and RX I/Q imbalances, and the multipath channel. With the obtained estimates, we can readily fulfill the compensation of I/Q imbalances. Unlike previous methods, which only estimate the combined effect of I/Q imbalances and the multipath channel, we are able to obtain the separate estimates of the TX I/Q imbalance, the RX I/Q imbalance and the multipath channel. This will significantly alleviate the computation burden of the proposed compensation scheme in the long run. Simulation results show that the proposed scheme outperforms the counterparts, and can significantly mitigate the adverse effects of I/Q imbalances.
6 citations
Cites background from "Frequency domain equalization for s..."
...Compared with OFDM, SC-FDE bears much lower peak-to-average power ratio (PAPR) of the modulated signal [2]....
[...]
11 Apr 2016
TL;DR: The importance of the channel independent PHY security techniques is highlighted, which target to protect the signal itself rather than encrypting the information bits.
Abstract: Security is one of the key requirements of wireless communication systems. By exploiting the broadcast nature of wireless medium, a malicious user might attempt to mislead the legitimate nodes, intercept the communication and overhear the private information. In order to combat against such malicious attacks, various encryption using security techniques have been proposed in the literature. Recently, physical layer (PHY) security has emerged as an additional countermeasure to the encryption based approaches and become very popular. Unlike cryptography, PHY security techniques target to protect the signal itself rather than encrypting the information bits. However, most of these techniques are designed based on specific channel conditions. Since channel has a random nature and cannot be controlled by users, such a design approach may remain unreliable for many practical scenarios where the desired channel state does not exist. Therefore, in this study, we highlight the importance of the channel independent PHY security techniques. In order to draft the ongoing efforts and provide the open issues in this direction, three different concepts are discussed along with the reviews of sample studies.
6 citations
Cites background from "Frequency domain equalization for s..."
...However, this technique requires a modified equalization with more complexity and leads to a bit of degradation of the BER performance specifically for OFDM....
[...]
...Basically, CP selection region is shifted towards the next SC-FDE or OFDM symbol by a positive random variable while the CP length is determined as much as the maximum excess delay (MED) of the channel and kept the same for all symbols....
[...]
...In [7], CP and pilot tones are completely discarded to suppress OFDM features and the inter-symbol interference is removed using a decision feedback equalizer....
[...]
...Time jitter can also be utilized in FH-OFDM signals to suppress the spectral lines at symbol and hopping periods....
[...]
...However, this approach eliminates the advantage of OFDM in handling multipath by using CP and introduces a considerable complexity....
[...]
10 Apr 2006
TL;DR: A new criterion called capacity criterion is proposed that can balance spectral and power efficiency, by which more information can be transmitted than by a former criterion called Gaussian criterion, though system bit error rate performance degrades.
Abstract: Based on the concept of optimal signal subspace, SC-FDE system could utilize the partial channel state information at the transmitter, so that system bit error rate performance can be improved considerably. However, the dimension of the optimal signal subspace is a critical parameter that links system spectral and power efficiency. In this paper, we propose a new criterion called capacity criterion that can balance spectral and power efficiency, by which more information can be transmitted than by a former criterion called Gaussian criterion, though system bit error rate performance degrades.
6 citations
21 Nov 2011
TL;DR: This dissertation deals with the design and development of baseband processing techniques for communication devices operating at a carrier frequency around 60 GHz and investigates the possibility of using low cost and complexity RF level diversity combining schemes to boost the system performance.
Abstract: Over the last couple of decades, wireless communication has proved to be a phenomenal success and has generated a booming industry with over 5 billion mobile handsets in use worldwide. This has on one end eased the life of its users while on the other end has introduced new challenges for wireless system designers. The varying nature of the wireless communication channel results in large differences in the instantaneous received signal strength. Since most mobile terminals are battery powered and operate in a network, simply increasing the transmission power is not an attractive solution, as it reduces the battery life and increases interference. Thus a major challenge in wireless communication is to increase the communication rate and link reliability by utilizing low power, low cost and spectrally efficient systems. Even with the advent of efficient signal processing techniques and miniaturized low power signal processing hardware, the physical bottleneck still remains the available system bandwidth. This has led to the introduction of the 60 GHz band as an attractive alternative. Among other benefits, the 60 GHz band is unlicensed and can provide system bandwidths up to 7 GHz, which is ideally suited for short range indoor wireless services such as wireless local area networks. There are, however, certain challenges that need to be overcome before full potential of 60 GHz band can be harnessed. These challenges include the design of hardware components such as antennas, amplifier and mixers, identification and utilization of suitable base band processing algorithms and efficient communication protocols for wireless networks operating in the 60 GHz domain. This dissertation deals with the design and development of baseband processing techniques for communication devices operating at a carrier frequency around 60 GHz. Firstly, two practical candidates for baseband implementation are identified. The performance of these two alternatives namely single-carrier and multi-carrier is analyzed under various radio frequency circuit imperfections such as phase noise and amplifier non-linearity because low cost radio frequency circuits operating in the 60 GHz band are expected to have less than ideal performance. For both schemes, the performance degradation in terms of operating parameters such as the required number of bits in digital-to-analog converter/analog-to-digital converter and input back-off requirements for the power amplifier as a function of bit error probability, is determined. It is shown that the single-carrier schemes suffer a lower degradation in system performance for a given set of circuit parameters. The single-carrier scheme is therefore, identified as a suitable candidate for 60 GHz baseband implementation. Secondly, we investigate the possibility of using low cost and complexity RF level diversity combining schemes to boost the system performance. Three low complexity diversity combining schemes namely equal gain combining, selection combining and switched combining are considered. An analytical framework for system performance evaluation of different diversity combining schemes by using low complexity RF level quantized phase combining is developed. Analytical expressions for the bit and symbol error rate of multi-level phase shift keying modulated symbols over Rayleigh fading channels are derived. The derived expressions are then utilized to compare the performance with non-coherent schemes under diversity reception. It is shown that the number of quantization levels required to achieve near ideal performance are dependent on the number of the receive antennas and the modulation level. The analysis is also utilized to investigate the impact of phase quantization on the switching threshold for switched combining schemes. It is shown that the switching threshold is not severely affected by phase quantization. The ability to perform various system level trade-offs is also demonstrated. Lastly, a low cost audio demonstrator is proposed. The acoustic channels investigated in this thesis are seen to provide a multi-path rich environment typical of 60 GHz channels. This offers a practical way of verifying the performance of various baseband processing algorithms in a cost effective manner.
6 citations
Cites background from "Frequency domain equalization for s..."
...In this regards, it is vital to investigate the impact of various RF level circuit imperfections on SC-FDE and MC schemes....
[...]
...The SC-FDE scheme with both phase shift keying and quadrature amplitude modulations was shown to require a lower input back-off (IBO) for the high power amplifier (HPA) and has a similar sensitivity to phase noise (PN) and in-phase/quadrature-phase (I/Q) imbalance for IEEE 802.11 transmission scenarios [38]....
[...]
...Therefore, a comparison of both SC-FDE and OFDM schemes under realistic 60 GHz RF front end and transmission scenarios is imperative for system design purposes....
[...]
...The SC-FDE scheme is known to achieve maximum diversity under frequency selective fading conditions [36], and therefore outperforms the MC scheme in un-coded scenarios....
[...]
...SC-FDE has a lower peak-to-average-power ratio (PAPR), and is more resistant to frequency offset errors as compared to the multi-carrier scheme [36]....
[...]
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]....
[...]
...Overlap-save or overlap-add signal processing techniques could also be used to avoid the extra overhead of the cyclic prefix [Fer85], [Hay96]....
[...]
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 ]....
[...]
...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 ]....
[...]
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