Near-Capacity Turbo Coded Soft-decision Aided DAPSK/Star-QAM for Amplify-and-Forward based Cooperative Communications

Multilevel Differential Amplitude and Phase-Shift Keying (DAPSK) schemes do not require any channel estimation, which results in low complexity. In this treatise we derive the soft-output probability formulas required for a soft-decision based demodulation of high-order DAPSK, in order to facilitate iterative detection by exchanging extrinsic information with an outer Turbo Code (TC). Furthermore, when the TC block size is increased, the system operates closer to the channel capacity. Compared to the identical-throughput TC assisted 64-ary Differential Phase-Shift Keying (64-DPSK) scheme, the 4-ring based TC assisted 64-ary DAPSK arrangement has a power-efficiency improvement of 2.3 dB at a bit error rate (BER) of 10-5 . Furthermore, when the TC block size is increased, the system operates closer to the channel capacity. More specifically, when using a TC block length of 400 modulated symbols, the 64 DAPSK (4, 16) scheme is 7.56 dB away from its capacity curve, while it had a reduced gap as low as 2.25 dB, when using a longer TC block length of 40 000 modulated symbols. Finally, as a novel application example, the soft-decision M-DAPSK scheme was incorporated into an Amplify-and-Forward (AF) based cooperative communication system, which attains another 4.5 dB SNR improvement for a TC block length of 40 000 modulated symbols

Reduced-complexity non-coherent soft-decision-aided DAPSK dispensing with channel estimation

Differential Amplitude Phase Shift Keying (DAPSK), which is also known as star-shaped QAM has implementational advantages not only due to dispensing with channel estimation, but also as a benefit of its low signal detection complexity. It is widely recognized that separately detecting the amplitude and the phase of a received DAPSK symbol exhibits a lower complexity than jointly detecting the two terms. However, since the amplitude and the phase of a DAPSK symbol are affected by the correlated magnitude fading and phase-rotations, detecting the two terms completely independently results in a performance loss, which is especially significant for soft-decision-aided DAPSK detectors relying on multiple receive antennas. Therefore, in this contribution, we propose a new soft-decision-aided DAPSK detection method, which achieves the optimum DAPSK detection capability at a substantially reduced detection complexity. More specifically, we link each a priori soft input bit to a specific part of the channel's output, so that only a reduced subset of the DAPSK constellation points has to be evaluated by the soft DAPSK detector. Our simulation results demonstrate that the proposed soft DAPSK detector exhibits a lower detection complexity than that of independently detecting the amplitude and the phase, while the optimal performance of DAPSK detection is retained

Soft-decision multiple-symbol differential sphere detection and decision-feedback differential detection for differential QAM dispensing with channel estimation in the face of rapidly fading channels

Turbo detection performed by exchanging extrinsic information between the soft-decision QAM detector and the channel decoder is beneficial for the sake of exploring the bit dependency imposed both by modulation and by channel coding. However, when the soft-decision coherent QAM detectors are provided with imperfect channel estimates in rapidly fading channels, they tend to produce potentially unreliable LLRs that deviate from the true probabilities, which degrades the turbo detection performance. Against this background, in this paper, we propose a range of new soft-decision multiple-symbol differential sphere detection (MSDSD) and decision-feedback differential detection (DFDD) solutions for differential QAM (DQAM), which dispense with channel estimation in the face of rapidly fading channels. Our proposed design aims for solving the two inherent problems in soft-decision DQAM detection design, which have also been the most substantial obstacle in the way of offering a solution for turbo detected MSDSD aided differential MIMO schemes using QAM: 1) how to facilitate the soft-decision detection of the DQAM's amplitudes, which-in contrast to the DPSK phases-do not form a unitary matrix, and 2) how to separate and streamline the DQAM's soft-decision amplitude and phase detectors. Our simulation results demonstrate that our proposed MSDSD aided DQAM solution is capable of substantially outperforming its MSDSD aided DPSK counterpart in coded systems without imposing a higher complexity. Moreover, our proposed DFDD aided DQAM solution is shown to outperform the conventional solutions in literature. Our discussions on the important subject of coherent versus noncoherent schemes suggest that compared to coherent square QAM relying on realistic imperfect channel estimation, MSDSD aided DQAM may be deemed as a better candidate for turbo detection assisted coded systems operating at high Doppler frequencie

Multiple-symbol differential sphere detection and decision-feedback differential detection conceived for differential QAM

Multiple-Symbol Differential Sphere Detection (MSDSD) relies on the knowledge of channel correlation. More explicitly, for Differential PSK (DPSK), the transmitted symbols’ phases form a unitary matrix, which can be separated from the channel’s correlation matrix by the classic Multiple-Symbol Differential Detection (MSDD), so that a lower triangular matrix extracted from the inverted channel correlation matrix is utilized for the MSDSD’s sphere decoding. However, for Differential QAM (DQAM), the transmitted symbols’ amplitudes cannot form a unitary matrix, which implies that the MSDD’s channel correlation matrix becomes amplitude-dependent and remains unknown, unless all the data-carrying symbol amplitudes are detected. In order to tackle this open problem, in this paper, we propose to determine the MSDD’s non-constant amplitudedependent channel correlation matrix with the aid of a sphere decoder, so that the classic MSDSD algorithms that were originally conceived for DPSK may also be invoked for DQAM detection. As a result, our simulation results demonstrate that the MSDSD aided DQAM schemes substantially outperform their DPSK counterparts. However, the price paid is that the detection complexity of MSDSD is also significantly increased. In order to mitigate this, we then propose a reduced-complexity MSDSD search strategy specifically conceived for DQAM constellations, which separately map bits to their ring-amplitude index and phase index. Furthermore, the classic Decision-Feedback Differential Detection (DFDD) conceived for DQAM relies on a constant channel correlation matrix, which implies that these DFDD solutions are sub-optimal and they are not equivalent to the optimum MSDD operating in decision-feedback mode. With the advent for solving the open problem of MSDSD aided DQAM, we further propose to improve the conventional DFDD aided DQAM solutions in this paper

Comparison of traffic performance of QPSK and 16-QAM modulation techniques for OFDM system, Journal of Telecommunications and Information Technology, 2005, nr 1

Orthogonal frequency division multiplexing (OFDM) provides better spectral efficiency than frequency division multiplexing (FDM), while maintaining orthogonal relation between carriers; hence traffic is better carried by OFDM than FDM within the same spectrum. This paper reveals a comparison of spectral efficiency, performance of communication system in context of bit error rate (BER) for the same information rate and peak to average power ratio (PAPR) of quadrature amplitude shift keying (QPSK) and 16-quadrature amplitude modulation (16-QAM) technique

OFDM Receiver Performance with Measured Channel Model in Power Line Communications

본 논문에서는 홈 네트워크의 중요한 구성 요소인 전력선 통신을 위한 채널 측정 방법을 소개하고 측정된 채널을 기반으로 하는 전력선 시스템의 성능 분석을 수행한다. 먼저 전력선 통신의 표준화 동향을 살펴보고, 다음으로 전력선 채널을 측정하기 위한 방법을 소개한 후, 전력선 채널 모델을 제시한다. 측정된 채널을 기반으로 OFDM 방식의 HomePlug 1.0 표준과 전송 속도 향상을 위해 제안된 전송 기술의 성능을 분석한다. 이러한 기술들은 전력선 통신을 위한 표준에 적용되어 전력선 통신 용량 증대 및 커버리지 확대에 기여할 것으로 예상된다.This paper reports the results of wideband channel measurements conducted on in house outlets. Two kinds of channel measurements were performed: impulse response measurements and noise signal measurements. In measure based channel model, preamble assisted orthogonal frequency-division multiplexing access (OFDM) receiver scheme is proposed for differential phase shift keying (DPSK) and quadrature amplitude modulation (QAM). Timing synchronization and channel estimation is performed using the preamble. We provide numerical results to illustrate the performance of OFDM receiver in measure based channel model.대학 IT연구센터 육성, 지원사

Performance of IEEE 802.11a wireless LAN standard over frequency-selective, slowly fading Nakagami channels in a pulsed jamming environment

Wireless local area networks (WLAN) are increasingly important in meeting the needs of the next generation broadband wireless communication systems for both commercial and military applications. In 1999, the Institute of the Electrical and Electronics Engineers (IEEE) 802.11a working group approved a standard for a 5 GHz band WLAN that supports a variable bit rate from 6 to 54 Mbps, and orthogonal frequency-division multiplexing (OFDM) was chosen because of its well-known ability to avoid multipath effects while achieving high data rates by combining a high order sub-carrier modulation with a high rate convolutional code. This thesis investigates the performance of the OFDM based IEEE.802.11a WLAN standard in frequency-selective, slowly fading Nakagami channels in a pulsed-noise jamming environment. Contrary to expectations, the signal-to-interference ratio (SIR) required to achieve a specific does not monotonically decrease when the bit rate decreases. Furthermore, the results show that the performance is improved significantly by adding convolutional coding with Viterbi decoding, and thus highlights the importance of forward error correction (FEC) coding to the performance of wireless communications systems.http://archive.org/details/performanceofiee109453638Lieutenant Junior Grade, Turkish NavyApproved for public release; distribution is unlimited

Multiuser MIMO-OFDM for Next-Generation Wireless Systems

This overview portrays the 40-year evolution of orthogonal frequency division multiplexing (OFDM) research. The amelioration of powerful multicarrier OFDM arrangements with multiple-input multiple-output (MIMO) systems has numerous benefits, which are detailed in this treatise. We continue by highlighting the limitations of conventional detection and channel estimation techniques designed for multiuser MIMO OFDM systems in the so-called rank-deficient scenarios, where the number of users supported or the number of transmit antennas employed exceeds the number of receiver antennas. This is often encountered in practice, unless we limit the number of users granted access in the base station’s or radio port’s coverage area. Following a historical perspective on the associated design problems and their state-of-the-art solutions, the second half of this treatise details a range of classic multiuser detectors (MUDs) designed for MIMO-OFDM systems and characterizes their achievable performance. A further section aims for identifying novel cutting-edge genetic algorithm (GA)-aided detector solutions, which have found numerous applications in wireless communications in recent years. In an effort to stimulate the cross pollination of ideas across the machine learning, optimization, signal processing, and wireless communications research communities, we will review the broadly applicable principles of various GA-assisted optimization techniques, which were recently proposed also for employment inmultiuser MIMO OFDM. In order to stimulate new research, we demonstrate that the family of GA-aided MUDs is capable of achieving a near-optimum performance at the cost of a significantly lower computational complexity than that imposed by their optimum maximum-likelihood (ML) MUD aided counterparts. The paper is concluded by outlining a range of future research options that may find their way into next-generation wireless systems