Xiaoming Peng

Directional Cooperative MAC Protocol Design and Performance Analysis for IEEE 802.11ad WLANs

In this paper, we consider the directional multigigabit (DMG) transmission problem in IEEE 802.11ad wireless local area networks (WLANs) and design a random-access-based medium access control (MAC) layer protocol incorporated with a directional antenna and cooperative communication techniques. A directional cooperative MAC protocol, namely, D-CoopMAC, is proposed to coordinate the uplink channel access among DMG stations (STAs) that operate in an IEEE 802.11ad WLAN. Using a 3-D Markov chain model with consideration of the directional hidden terminal problem, we develop a framework to analyze the performance of the D-CoopMAC protocol and derive a closed-form expression of saturated system throughput. Performance evaluations validate the accuracy of the theoretical analysis and show that the performance of D-CoopMAC varies with the number of DMG STAs or beam sectors. In addition, the D-CoopMAC protocol can significantly improve system performance, as compared with the traditional IEEE 802.11ad MAC protocol.

Performance studies of a multi-band OFDM system using a simplified LDPC code

Ultra-wideband (UWB) is a promising radio technology for networks delivering extremely high data rates at short ranges. Multi-band orthogonal frequency division multiplexing (MB-OFDM) is a suitable solution to implement high speed data in ultra wideband spectrum by dividing the available spectrum into multiple bands. MB-OFDM achieves adaptability as well as high performance, low-power and low-cost characteristics through the usage of OFDM. Due to the importance of error correcting codes for OFDM systems, it is essential to employ a powerful error correcting code for the MB-OFDM system to improve the performance. Recently, low-density parity-check (LDPC) code has attracted great attention because it achieves bit error rate near to the Shannon limit. In this paper, we design and evaluate the performance of the MB-OFDM system using LDPC code. In order to simplify the implementation of the LDPC encoder and decoder, we introduce a joint code and decoder design approach to construct a class of (3, k)-regular LDPC code which exactly fits to a partly parallel decoder implementation. The simulations show that the performance of such a simplified LDPC coded MB-OFDM system is better than that of a convolutional coded MB-OFDM system, and is very close to that of the conventional LDPC coded MB-OFDM system. The implementation complexity of the simplified LDPC code is carefully examined subsequently in the paper.

A simplified transceiver structure for cyclic extended CDMA system with frequency domain equalization

In this paper, a new cyclic-extended block-spreading CDMA (CEBS-CDMA) system is proposed to combat multiple access interference (MAI) efficiently over a frequency selective fading channel for an asynchronous reverse link transmission. Attribute to the block spreading, the MAI is minimized due to the small channel variation across consecutive blocks in a typical high speed system, where the signaling block duration is very short. It suggests a simplified transceiver structure with symbol-wise efficient frequency domain equalization (FDE) to improve the performance and reduce the complexity under frequency selective fading channels. A new cell-specific scrambling code is proposed with the CEBS-CDMA system for a multi-cell environment reverse link transmission, suppressing other-cell interference (OCI) efficiently. The simulation results show that the proposed CEBS-CDMA system achieves much better performance of multiple users compared to the conventional direct sequence CDMA (DS-CDMA) and cyclic prefix-CDMA systems.

Ranging Mechanism, Preamble Generation, and Performance with IEEE 802.15.4a Low-Rate Low-Power UWB Systems

IEEE 802.15.4a task group is defining an ultra low power consumption and low cost radio for wireless personal area networks (WPANs) applications using ultra-wideband (UWB) technology with high precision ranging capability. Ternary preamble sequences of two different lengths have been proposed and adopted in the IEEE 802.15.4a specification for ranging. In order for a IEEE 802.15.4a low cost UWB device to support multiple frequency bands across the available spectrum and ranging features, as many as twenty-four ternary sequences is required. A sizeable amount of memory is needed to store the codes. In this paper, we propose a method to generate the ternary codes using linear feedback shift registers (LFSRs) as and when it is required, resulting in significant memory savings. The ranging performance using the proposed ternary preamble sequence is evaluated through simulation

Kronecker Modelling for Correlated Shadowing in UWB MIMO Channels

The shadowing in ultra wideband (UWB) channels may degrade the system performance significantly. Although UWB multipath channels exhibit high resolution in space and time. The large scale shadow fading were moderately correlated based on UWB indoor channel measurement. In this paper, a new modelling method for correlated shadowing with log-normal distribution in UWB multiple-input multiple-output (MIMO) channels is proposed based on the Kronecker model and IEEE 802.15.3a channel model recommendation. Moreover, antenna selection technique with low hardware complexity is proposed for a UWB system with multiple receive or transmit antennas to mitigate its channel shadowing effect. The BER performance for orthogonal frequency division multiplexing (OFDM) UWB system with power based antenna selection is evaluated. Antenna selection technique is shown to be effective in mitigating the correlated shadow fading.

Spatial reuse strategy in mmWave WPANs with directional antennas

In this paper, we propose a spatial reuse strategy for millimeter-wave (mmWave) wireless personal area networks (WPANs) with directional antennas. By this strategy, two or more transmissions can be appropriately scheduled for spatial sharing based on the beamforming (BF) information. Moreover, we analyze the performance of this strategy with consideration of the difference between idealistic and realistic directional antennas. Simulation results show that the strategy efficiency is related to antenna types, configurations and network topologies, and that the spatial multiplexing gain can be increased accordingly.

Joint carrier and sampling frequency offset estimation for MB-OFDM UWB system

In this paper, a novel joint carrier and sampling frequency offset estimation scheme for multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra wideband (UWB) system is introduced. We investigate the relationship between carrier and sampling frequency offset when they have a common error source and derive the joint estimation scheme. The proposed scheme consists of two stages. In the first stage, a robust estimation of the frequency offset is carried out using preamble symbols. In the second stage, pilot subcarriers within OFDM symbols is used to track the phase distortion caused by the presence of estimation error, if any, in the first stage. Extensive simulation is carried out and the results show that when coupled with the appropriate compensation algorithms, the proposed scheme is effective in limiting the MB-OFDM system performance degradation due to frequency offset to within 0.5 dB.

An integrated 60GHz low power two-chip wireless system based on IEEE802.11ad standard

This paper presents our developed two-chip wireless communication system adhering to the IEEE 802.11ad standards with a baseband IC (BBIC) integrated with a low power 60 GHz transceiver SOC (RFIC) and antennas. The novel low power 60GHz RFIC using a sub-harmonic sliding-IF scheme is fully integrated based on low cost SiGe 0.18 um BiCMOS process. The BBIC uses an adaptive time domain equalizer rather than the commonly used frequency domain equalizer to lower the requirements on power consumption.

Block Spread IFDMA: An Improved Uplink Transmission Scheme

In this paper, a block-spread interleaved frequency division multiple access (BS-IFDMA) scheme is proposed. It is capable of allocating users in block-level code-spreading process for multiple access on top of the IFDMA multiple access scheme for better user allocation. Orthogonality among users in block spreading is achieved when the block spreading, carried out in the time domain, is over a few IFDMA block symbols with negligible channel variation (i.e. transmission over quasi time-invariant channel). Given the same number of supported users and same system bandwidth, by allocating more users in the block level code spreading domain, more frequency diversity can be achieved for the proposed scheme since more subcarriers can be allocated to individual user in the frequency domain compared to the conventional IFDMA scheme.

Outage Performance of Relaying with Directional Antennas in the Presence of Co-Channel Interferences at Relays

Relaying with directional antennas helps enhance the link reliability and extend the communication range for millimeter wave 60GHz communication system, particularly in the presence of multiple co-channel interferences (CCIs). In this letter, the outage performance of decode-and-forward (DnF) and amplify-and-forward (AnF) relaying schemes with directional antennas are analyzed and compared. Our derived exact and closed-form expressions using Moschopouloss gamma series in the presence of multiple CCIs with dissimilar Nakagami fading channels at relays offer more accurate analytic result with practically computational efficiency. Numerical results show that relaying with directional antennas, in the forms of uniformly spaced linear antenna arrays, helps improve the system performance significantly in the presence of CCIs.