Umar H. Rizvi

Robust 60 GHz Indoor Connectivity: Is It Possible with Reflections?

In this paper, we investigate the robustness of the 60 GHz connectivity in typical indoor environments by analyzing the outage probability. We define three realistic indoor scenarios which may host the 60 GHz networks in the future and perform simulations with a verified 3D ray tracing tool on them. In the first set of simulations, we show the impact of access unit position on the connectivity. In the next step, we show that increasing the obstacle density linearly decreases the outage probability of the 60 GHz network and this decrease is found to be sharper for certain positions of the access point. In the last step, we demonstrate the direct effect of reflective surface availability on the connectivity. A 60 GHz indoor network relying solely on the reflections in the absence of line-of-sight path is very vulnerable to outages even in moderately populated indoor environments.

Impact of RF circuit imperfections on multi-carrier and single-carrier based transmissions at 60 GHz

Circuit technology for 60 GHz is still limited, and impairments due to radio frequency (RF) circuit imperfections must be taken into account. Therefore, the candidate transmission schemes, in addition to multi-path fading, should be fairly resistant to RF circuit imperfections. In this paper, a performance comparison of multi-carrier (MC) and single-carrier (SC) based transmission schemes in the presence of DAC/ADC imperfections and amplifier nonlinearities, is carried out. It is shown that the SC scheme has substantially lower front-end requirements than its MC counterpart, while having the same overall system complexity.

Rotation Optimization for MPSK/MQAM Signal Constellations Over Rayleigh Fading Channels

The performance of uncoded phase-shift-keying (PSK) and quadrature amplitude modulation (QAM) schemes over fading channels can be improved by using coded modulation techniques. Improvement is due to the coding gain coupled with interleaving and depends on the complexity of the code. Recently, it was shown that constellation rotation coupled with interleaving can be used to improve the performance of QPSK modulation over block-fading single-input-single-output (SISO) wireless communication channels. This paper considers the use of such a scheme with higher order constellation sets such as 8PSK and 16QAM. A framework is then presented for the calculation of the optimum rotation angle for MPSK/MQAM schemes. A simple cost function based on the union bound of the symbol error probability (SEP) is defined. The optimum rotation angle is then found by minimizing the cost function using the gradient search algorithm. The obtained simulation results show considerable improvement over the conventional unrotated system

Optimized Rotations for LDPC-Coded MPSK Constellations with Signal Space Diversity

For multi-level modulation methods, rotation of the signal constellation together with in-phase and quadrature phase channel interleaving (signal space diversity) are known to provide good performance gains over fading channels. This paper studies the extension of such schemes with a low density parity check (LDPC) code. It is shown that for both coded and uncoded Gray-mapped MPSK modulation formats with signal space diversity on a Rayleigh fading channel, a well-considered choice of the rotation angle may lead to a significant gain over the conventional unrotated constellation. However, the optimum rotation angle for the coded scheme may be different from the corresponding optimization angle of the uncoded scheme.

Impact of RF Impairments on the Performance of Multi-carrier and Single-carrier based 60 GHz Transceivers

The 60 GHz band, with a large unlicensed bandwidth, is an excellent choice for short distance high-speed communications. However, radio frequency (RF) circuit limitations at 60 GHz give rise to impairments such as phase noise, in-phase/quadrature-phase (I/Q) imbalance and amplifier nonlinearities. The candidate transmission schemes, in addition to multi-path fading, should therefore be fairly robust against RF circuit imperfections. This paper investigates the performance degradation as a function of various circuit parameters for multi-carrier (MC) and single-carrier (SC) schemes, which can be useful for:( i) performing a system cost and performance tradeoff comparison, (ii) identifying main performance bottle necks for MC and SC based systems.

Performance of Equal Gain Combining with Quantized Phases in Rayleigh Fading Channels

In this paper, we analyze the error probability of equal gain combining with quantized channel phase compensation for binary phase shift keying signalling over Rayleigh fading channels. The probability density and characteristic functions of the combined signal amplitude are derived and used to compute the analytic expressions for the bit error probability in dependance of the number of quantization levels L, the number of diversity branches NR and the average received signal-to-noise ratio. The analysis is utilized to outline the trade-off between NR and L and to compare the performance with non-coherent binary frequency shift keying and differential binary phase shift keying schemes under diversity reception.

Cooperative Communications in Future Home Networks

The basic idea behind cooperative communications is that mobile terminals collaborate to send data to each other. This effectively adds diversity in the system and improves the overall performance. In this paper, we investigate the potential gains of cooperative communication in future home networks. We derive analytical expressions for the error probability of binary phase shift keying (BPSK) signals over Nakagami-m fading channels in a multi relay communication network. Following to the analytical study, we analyze the contribution of cooperative relaying to the 60GHz network connectivity through simulations using a realistic indoor environment model. We compare the performance of different relay configurations under variable obstacle densities. We show that a typical 60GHz indoor network should employ either a multi-relay configuration or a single-relay configuration with a smart relay selection mechanism to achieve acceptable outage rates. In the use of multiple-relay configuration, both analytical and simulation studies indicate that increasing the number of cooperative relays does not improve the system performance significantly after a certain threshold.

BER analysis for MPAM signal constellations in the presence of fading and ADC quantization noise

In this letter, closed-form expressions for the bit error rate of M-ary pulse amplitude modulated signal constellations as a function of the analog-to-digital converter word length, the signal-to-noise ratio and the fading distribution, are derived. These results allow for a rapid and accurate evaluation of the system performance when the analog-to-digital converter resolution is limited, as is generally the case in high sampling rate communication systems, and thus provide a useful tool for system design, analysis and optimization.

Modulation diversity benefits in cooperative communications

In this paper we propose modulation diversity as a candidate diversity scheme for uncoded cooperative communication in wireless networks with decode-and-forward (DF) communication protocol. A performance analysis of such a scheme in Nakagami-m fading channels in the presence of additive white Gaussian noise (AWGN) is presented. An upper bound on the average probability of bit error (Pb) and average probability of symbol error (Ps) is derived for M-ary phase shift keying (MPSK) modulation schemes. It is shown that the system employing employing modulation diversity is able to provide a performance improvement of 5 dB at a bit error rate of 10−4 as compared to the conventional cooperative communication systems. We introduce a power allocation factor and show that equal power allocation is not the optimal solution. Furthermore, we also analyze the effect of different rotation angles and power allocation on the system performance.

Optimized Rotations for LDPC-coded Gray-mapped MPSK Constellations with Signal Space Diversity

Rotation of the signal constellation together with in-phase and quadrature channel interleaving (signal space diversity) is known to provide good performance gains over fading channels for multi level modulation methods. This paper studies the extension of such schemes with a low density parity check (LDPC) code. It is shown that for both coded and un-coded Gray-mapped MPSK modulation formats with signal space diversity on a Rayleigh fading channel, a well-considered choice of the rotation angle may lead to a significant gain over the conventional un-rotated constellation. However, the optimum rotation angle for the coded scheme may be different from the corresponding optimization angle of the un-coded scheme