Mohd Riduan Ahmad

Performance analysis of MAC protocol for cooperative MIMO transmissions in WSN

Cooperative Multi-In Multi-Out (MIMO) schemes can reduce both transmission energy and latency in distributed wireless sensor networks (WSNs). When circuit energy is considered in such networks, the total energy consumed as the number of cooperating nodes increases becomes of particular interest. In addition, most of the previous works focused only on space-time-block-code (STBC) schemes and ignore other MIMO schemes. In this paper we present a comparison study of three cooperative MIMO schemes: beamforming (BF), STBC and spatial multiplexing (SM) where both the transmission and circuit energies are considered. We consider a wireless sensor network operating in quasi-static Rayleigh fading channels with M cooperating transmit nodes and N cooperating receive nodes. We show that the single-in-single-out (SISO) scheme is more energy-efficient and has lower packet latency at higher regions of transmission power while the three cooperative MIMO schemes are more energy-efficient and outperform the SISO scheme at the lower regions. From our analysis, we can conclude that, beamforming outperforms both the SM and STBC schemes in term of energy-efficiency and lower packet latency. Also we suggest that the beamforming scheme utilising two transmit nodes results in an efficient cooperative system.

MIMO beamforming network having polarization diversity

This paper presents a MIMO channel measurement for indoor environment. The results present the comparison of channel capacity by using beamforming technique in MIMO systems. Also, polarization diversities (vertical and horizontal) are introduced to reduce multipath fading issues. The measurements were conducted at 2.4GHz with Line of Sight (LOS) scenario.

Performance evaluation of MAC protocols for cooperative MIMO transmissions in sensor networks

Cooperative Multiple-Input Multiple-Output (MIMO) schemes can reduce both transmission energy and latency in distributed wireless sensor networks (WSNs). In this paper we develop a new cooperative low power listening (LPL) Medium Access Control (MAC) protocol for two cooperative MIMO schemes: optimal Beamforming (BF) and Spatial Multiplexing (SM). We develop analytical models for the total energy consumption and retransmission rates for both schemes and analyse the proposed MAC protocol in term of total energy consumption. The impact of the check interval and the number of cooperative transmitting nodes, M and cooperative receiving nodes N on the total energy consumption are investigated. We show that the new cooperative MAC with the optimal Beamforming scheme outperforms the other cooperative and SISO schemes in term of total energy consumption with the number of cooperating nodes set to M=2.

MAC Protocol for Cooperative MIMO Transmissions in Asynchronous Wireless Sensor Networks

Cooperative MIMO schemes can reduce both transmission energy and latency in distributed wireless sensor networks (WSNs). In this paper we develop a new cooperative low power listening (LPL) medium access control (MAC) protocol for two cooperative MIMO schemes: optimal beamforming (BF) and spatial multiplexing (SM). We develop analytical models for the total energy consumption and packet latency for both schemes and analyse the proposed MAC protocol in term of the total energy consumption and packet latency with imperfect synchronisation due to clock jitter. The impact of the clock jitter, the check interval and the number of cooperative nodes on the total energy consumption and latency are investigated. We observe that the cooperative LPL MAC with Optimal BF is the most promising configuration and it is optimal when then number of co-operating nodes M=2 and jitter difference is below 0.6 Tb.

BER-delay characteristics analysis of IEEE 802.15.4 wireless sensor networks with cooperative MIMO

This paper presents a study of the impact of transmission delay differences between co-operating nodes on bit error rate performance and energy consumption of wireless sensor networks. We consider a wireless sensor network using an Alamouti virtual MIMO (multiple-input multiple-output) configuration between collaborating nodes operating in quasi-static Rayleigh flat-fading channels. Our results show that above certain delay difference (in the range above 0.75Tb), the traditional non-cooperative approach is more energy-efficient than the cooperative strategy and that the transmission delay difference has the most significant on the transmission energy consumption in the delay range of below 0.75Tb.

Concurrent MAC with Short Signaling for multi-hop Wireless Mesh Networks

The IEEE 802.11 Distributed Coordination Function (DCF) Medium Access Control (MAC) protocol continues to suffer from throughput degradation when directly applied in multi-hop Wireless Mesh Network (WMN). The Request-to-Send/Clear-to-Send (RTS/CTS) signaling partially solved hidden node problems however the exposed node problems remain unaddressed. The IEEE 802.11 MAC does not allow the exposed nodes to initiates its transmission for the entire duration of ongoing transmission over multi-hop network leads to throughput degradation. Moreover, the amount of needed signaling packets takes place at every hop reduces the overall multi-hop throughput significantly. This project proposes a set of enhancement to the existing IEEE 802.11 DCF MAC by enabling concurrent transmission by the exposed nodes and reduces the amount of signaling packets (CMAC-SS) required at every hop until the data packet reaches its destination. Analytical models are developed and simulated over quasi-static Rayleigh fading channel. The multi-hop network performances are evaluated in terms of throughput and delay. The CMAC-SS protocol outperforms the existing IEEE DCF MAC with more than 14% increase in overall throughput of multi-hop WMN.

Physical and MAC Cross Layer Design for Wireless Mesh Networks

Wireless mesh networks (WMNs) are an alternative technology for last-mile broadband Internet access that can support broadband services. However, for a WMN to be all it can be, considerable research efforts are still needed. For example, the available MAC and routing protocols are not scalable; throughput drops significantly as the number of nodes or hops in WMNs increases. Thus, existing protocols need to be enhanced or re-invented for WMNs. When advanced physical layer techniques, used, novel MAC protocols, especially multi-channel MAC, need to be proposed to utilize the agility provided by the physical layer. This paper presents an introduction to wireless mesh networks, IEEE 802.11, physical layer and Medium Access Control (MAC) cross layer design.

Measurement of bit error rate at 2.4 GHz due to lightning interference

This paper analyzes the interference of lightning flashes with wireless communication systems operating in the microwave band at 2.4 GHz. A bit error rate (BER) measurement method was used to evaluate BER during 3 heavy thunderstorms on January 25, March 17 and March 20, all in year 2011. In addition, BER measurements also were done on January 21 and March 30, 2011 under fair weather (FW) conditions providing a baseline for comparison. The Transmitter-Receiver separation was fixed at 10 meter with line-of-sight (LOS) consideration. We infer that lightning interfered with the transmitted digital pulses which resulted in a higher recorded BER. The maximum recorded BER was 9.9·10-1 and the average recorded BER was 9.95·10-3 during the thunderstorms with the average fair weather BER values under the influence of adjacent channel interference (ACI) and co-channel interference (CCI) being 1.75·10-5 and 7.35·10-6 respectively. We conclude that wireless communication systems operating at 2.4 GHz microwave frequency can be significantly interfered by lightning.

Lightning Interference in Multiple Antennas Wireless Communication Systems

This paper analyzes the interference of lightning flashes with multiple antennas wireless communication systems operating in the microwave band at 2.4 GHz and 5.2 GHz. A bit error rate (BER) measurement method was used to evaluate BER and packet error rate (PER) during 5 heavy thunderstorms on January 25 and March 17 to 20, 2011, respectively. In addition, BER measurements also were done on January 21 and March 30, 2011 under fair weather (FW) conditions providing a baseline for comparison. The Transmitter-Receiver separation was fixed at 10 meter with line-of- sight (LOS) consideration. We infer that lightning interfered with the transmitted digital pulses which resulted in a higher recorded BER. The maximum recorded BER was 9.9·10 -1 and the average recorded BER and PER were 2.07·10 -2 and 2.44·10 -2 respectively during the thunderstorms with the average fair weather BER and PER values under the influence of adjacent channel interference (ACI) and co-channel interference (CCI) being 1.75·10 -5 and 7.35·10 -6 respectively. We conclude that multiple antennas wireless communication systems operating at the microwave frequency can be significantly interfered by lightning.

Chaotic pulse train in cloud-to-ground and cloud flashes of tropical thunderstorms

In this paper, we report for the first time the observation of chaotic pulse train (CPT) preceding natural subsequent negative return strokes and also CPT occurrence in IC flashes from tropical thunderstorms in South Malaysia. In CG flashes, all CPTs were occurred in between return strokes with 41.1% have occurred between the first and second return strokes. The maximum number of CPT in one sequence is 3, which can be observed between the first and third return strokes only. In IC flashes, all CPTs were observed to occur in between IC flash pulses.