Anshul Tyagi

A Survey on Various Coherent and Non-coherent IR-UWB Receivers

The recent developments in radio technologies, paves its way to impulse radio (IR) ultra-wideband (UWB) communication, which is used for low power, short range and high bandwidth communication, thereby exploiting a large portion of radio spectrum. In this paper, a brief review of the work done by various researchers on coherent and non-coherent IR-UWB receivers has been analysed, based on their bit error rate (BER) performances, as well as pros and cons of using these receivers. An in depth study on the receivers concludes that, non-coherent IR-UWB receiver is preferred over its counterpart coherent IR-UWB receiver even though it comes at the expense of poor BER performance. The simulation results prove that, though the performances are same, the low complexity of energy detector (ED) receivers gives an edge over the autocorrelation receivers. Further, ED receiver suffers from noise, which paves way to using weighted ED (WED) receiver. The superiority of WED receivers over all the other non-coherent UWB receivers is further confirmed by the simulation performed in AWGN and IEEE 802.15.4a UWB channels. It can also be concluded from the review that, some special receivers such as generalized likelihood ratio test, multi-symbol differential detector and decision feedback differential transmitted reference, when clubbed with UWB systems, lead to further improvement in BER performance.

Cooperative Impulse Radio Ultra-Wideband Communication Using Coherent and Non-Coherent Detectors: A Review

Ultra-wideband (UWB) is a booming technology in the field of wireless communication. This paper presents a brief idea related to the various coherent and non-coherent IR-UWB detectors. Due to the limitation in transmit power spectral density of UWB system, the major challenges faced by UWB system includes, achieving Quality of Service, system performance and coverage area. So, the combination of UWB system with cooperative communication will not only improve the system performance, but also help in expanding coverage area of signals. A brief review of the work done by various researchers in the field of cooperative impulse radio (IR) UWB communication is also presented in this paper. The working principle and performance analysis of the various coherent and non-coherent IR-UWB detectors using cooperative relay strategies are also discussed at large in this paper. The various fixed cooperative relay strategies used for cooperative UWB communication is Amplify and Forward, Decode and Forward and Detect and Forward. From the simulation results it can be inferred that, even though IR-UWB DTR receiver gives a much better BER performance than IR-UWB ED receiver using both cooperative and non-cooperative strategies, yet ED receiver is preferred because of its less complexity and low power consumption. Future prospects in the field of cooperative IR-UWB communication have also been discussed in this paper.

A New Distance Notion for PPAM Space--Time Trellis Codes for UWB MIMO Communications

We introduce a new distance notion and develop novel design criteria for optimal MN-ary pulse position amplitude modulation (PPAM) space-time trellis codes (STTC) for ultrawideband multiple-input multiple-output systems for slow and fast fading at both low and high SNR. Simulation results of the 2,2-ary PPAM STTC, constructed through set partitioning, confirm significant reduction in bit error rate.

Weighted Least Squares Based Spectral Precoder for OFDM Cognitive Radio

This letter presents a novel spectral precoding scheme for orthogonal frequency division multiplexing (OFDM) based cognitive radio (CR) systems. Unlike existing techniques, where the least squares approach leads to a biased solution causing more distortion on some subcarriers than others, the proposed precoder adopts a weighted least squares approach and uses Lawsons algorithm for obtaining desired weights. Simulation results show that the proposed precoder provides significant BER performance gain without much impact on computational complexity and sidelobe suppression. Moreover, the proposed precoder when combined with decision directed iterative decoding at the receiver provides bit error rate (BER) performance similar to that of an un-suppressed OFDM system.

Extended Subcarrier Weighting for Sidelobe Suppression in OFDM Based Cognitive Radio

Subcarrier weighting (SW) is a recognized technique for sidelobe suppression in OFDM systems. In this paper SW is discussed in the context of cognitive radios where some portion of the spectrum is shared with primary users so it is required to notch that portion. A major disadvantage with SW scheme is bit error rate (BER) degradation due to unequal power distribution among different subcarriers therefore the primary objective of the paper is to enhance the performance of SW without additional degradation in BER performance. To this extent we propose an Elliptical-SW scheme by expanding the locus of weights to elliptical region. Simulation results show that the proposed scheme can produce deeper notch as compared to Conventional-SW for same BER performance. In second part we present a Partial-SW scheme by applying SW to lesser number of subcarriers. It can enhance BER performance significantly with negligible loss in sidelobe suppression capacity. Another scheme namely Guarded-SW is also proposed in this paper to provide further means to obtain very deep notches without any additional degradation in BER however it has to scarify some throughput. Finally an effective way of implementing SW in MIMO systems is presented by jointly optimizing weights over selected number of antennas.

Antiphase Tones Across Transmitting Antennas: A Spectrum Sharing Technique for Cognitive CO-STFC MB-OFDM UWB System

This paper proposes a spectrum sharing technique for coexistence of multiband orthogonal frequency division multiplexing ultra wideband (UWB) system with other primary wireless services. Existing technique like tone nulling do not utilize subcarriers within victim band, hence affects the throughput of the system. The same nulling effect can be produced by applying antiphase tones across transmitting antennas and simultaneously utilizing the victim band to transmit the data. This scheme can be applied without any impact on the current specifications of the system. In this paper complex orthogonal space time frequency code is implemented to achieve diversity in multiple antenna system. UWB receiver processing is described for both victim and unprotected band. A less computationally complex active interference cancellation scheme is also applied to improve notch depth. The proposed scheme is implemented for fixed frequency interleaving operation and discussed for time frequency interleaving with special cases. The proposed scheme is very simple to implement and provide flexibility in terms of notch width and depth.

Performance analysis of TR, ATR and DTR receivers in IR-UWB communication system

Non-Coherent Ultrawideband (UWB) Autocorrelation (AR) Receivers require no channel state information, hence are preferred over coherent UWB receivers. The paper discusses the effectiveness of major UWB schemes using AR receivers: the Transmitted Reference (TR) scheme, Averaged Transmitted Reference (ATR) and Differential Transmitted Reference (DTR) scheme. Performance comparison using Matlab Simulation reveals that ATR and DTR receiver outperforms the conventional TR receiver by 3-4 dB both in AWGN and IEEE 802.15.4a environment.

Sidelobe suppression using differential coding in OFDM cognitive radios

Orthogonal frequency division multiplexing (OFDM) is a recognized transmission technique for Cognitive radio (CR) systems but one of the major drawback of OFDM scheme is its out-of-band (OOB) leakage due to high spectral sidelobes. In this paper we propose a sidelobe suppression technique using a differential coding. The concept working behind the scheme is polynomial-cancellation-coding (PCC) in which one data symbol is transmitted on group of subcarriers. The proposed scheme have advantageous results when information source produces symbols with unequal probabilities which may be the case in practical transmission. Unlike to the basic PCC scheme, the proposed technique does not affect the throughput of the system. The technique is very simple to implement. Simulation results show reduction in in-band and out-of-band spectrum leakage.

Performance analysis of non-coherent IR-UWB receivers

Non-Coherent Autocorrelation (AR) UWB receivers are preferred over coherent UWB receivers because it requires no channel state information (CSI) and hence is less complex in nature. The paper investigates the performance of Transmitted Reference (TR) and Differential Transmitted Reference (DTR) scheme using AR UWB receivers. Theoretical analysis of BER performance of non-coherent IR-UWB receivers is also discussed at large and compared with simulation results. Analytical and simulation results reveal that non-coherent IR-UWB DTR receiver outperforms TR receiver by a margin of 3-4 dB in AWGN and IEEE 802.15.4a UWB environment.

M-PAM space–time trellis codes for ultra-wideband multiple-input multiple-output communications

Multiple-input multiple-output (MIMO) systems with space-time (ST) coding are desirable in ultra- wideband (UWB) communication systems to improve the error-rate performance of the UWB link. The authors have considered the design of optimal (in error-rate performance) M-ary pulse-amplitude modulated (M-PAM) ST trellis codes (STTC) for a pulse-based UWB MIMO communication system. Following the approach by Vucetic et al. for narrowband systems, the authors carry out a probability of error analysis to derive upper bounds on pairwise symbol error probability for a UWB communication system for slow fading and fast fading at both low and high signal-to-noise ratios (SNRs). The authors deduce the design criteria from the upper bounds. Based on these criteria, an optimal four-state binary-PAM STTC, for two transmit antennas, is designed by hand. Finally, simulation results of the optimal binary-PAM STTC in a UWB communication system confirm significant improvement in bit error-rate performance over previously proposed ST coding scheme for UWB, at higher transmit SNR.