Investigation of VBLAST Equalization Technique for Underwater Acoustic Communications

Underwater Acoustic Communications (UWAC) is an emerging technology in the field of underwater communications, and it is challenging because of the signal attenuation of the sound waves. Multiple Input and Multiple-Output (MIMO) is introduced in UWAC because of its support in enhancing the data throughput even under the conditions of interference, signal fading, and multipath. The paper presents the concept and analysis of 2× 2 MIMO UWAC systems that uses a 4- QAM spatial modulation scheme thus minimizing the decoding complexity and overcoming the Inter Channel Interference (IChI). Bit Error Rate (BER) investigation is carried out over different link distances under acoustic Line of Sight (LOS). The utilization of Zero Forcing (ZF) and Vertical-Bell Laboratories Layered Space-Time (VBLAST) equalizers, which estimates the transmitted data proves a success of removing Inter Symbol Interference (ISI).  The ISI caused due to multipath effect and scattering in UWAC can be reduced by iterative process considered in VBLAST.  A study is made on how the distance between the transmitter and the receiver and the Doppler Effect has its impact on the performance of the system

Investigation of VBLAST Equalization Technique for Underwater Acoustic Communications

Underwater Acoustic Communications (UWAC) is an emerging technology in the field of underwater communications, and it is challenging because of the signal attenuation of the sound waves. Multiple Input and Multiple-Output (MIMO) is introduced in UWAC because of its support in enhancing the data throughput even under the conditions of interference, signal fading, and multipath. The paper presents the concept and analysis of 2× 2 MIMO UWAC systems that uses a 4- QAM spatial modulation scheme thus minimizing the decoding complexity and overcoming the Inter Channel Interference (IChI). Bit Error Rate (BER) investigation is carried out over different link distances under acoustic Line of Sight (LOS). The utilization of Zero Forcing (ZF) and Vertical-Bell Laboratories Layered Space-Time (VBLAST) equalizers, which estimates the transmitted data proves a success of removing Inter Symbol Interference (ISI).  The ISI caused due to multipath effect and scattering in UWAC can be reduced by iterative process considered in VBLAST.  A study is made on how the distance between the transmitter and the receiver and the Doppler Effect has its impact on the performance of the system

Physical and Link Layer Implications in Vehicle Ad Hoc Networks

Vehicle Ad hoc Networks (V ANET) have been proposed to provide safety on the road and deliver road traffic information and route guidance to drivers along with commercial applications. However the challenges facing V ANET are numerous. Nodes move at high speeds, road side units and basestations are scarce, the topology is constrained by the road geometry and changes rapidly, and the number of nodes peaks suddenly in traffic jams. In this thesis we investigate the physical and link layers of V ANET and propose methods to achieve high data rates and high throughput. For the physical layer, we examine the use of Vertical BLAST (VB LAST) systems as they provide higher capacities than single antenna systems in rich fading environments. To study the applicability of VB LAST to VANET, a channel model was developed and verified using measurement data available in the literature. For no to medium line of sight, VBLAST systems provide high data rates. However the performance drops as the line of sight strength increases due to the correlation between the antennas. Moreover, the performance of VBLAST with training based channel estimation drops as the speed increases since the channel response changes rapidly. To update the channel state information matrix at the receiver, a channel tracking algorithm for flat fading channels was developed. The algorithm updates the channel matrix thus reducing the mean square error of the estimation and improving the bit error rate (BER). The analysis of VBLAST-OFDM systems showed they experience an error floor due to inter-carrier interference (lCI) which increases with speed, number of antennas transmitting and number of subcarriers used. The update algorithm was extended to VBLAST -OFDM systems and it showed improvements in BER performance but still experienced an error floor. An algorithm to equalise the ICI contribution of adjacent subcarriers was then developed and evaluated. The ICI equalisation algorithm reduces the error floor in BER as more subcarriers are equalised at the expense of more hardware complexity. The connectivity of V ANET was investigated and it was found that for single lane roads, car densities of 7 cars per communication range are sufficient to achieve high connectivity within the city whereas 12 cars per communication range are required for highways. Multilane roads require higher densities since cars tend to cluster in groups. Junctions and turns have lower connectivity than straight roads due to disconnections at the turns. Although higher densities improve the connectivity and, hence, the performance of the network layer, it leads to poor performance at the link layer. The IEEE 802.11 p MAC layer standard under development for V ANET uses a variant of Carrier Sense Multiple Access (CSMA). 802.11 protocols were analysed mathematically and via simulations and the results prove the saturation throughput of the basic access method drops as the number of nodes increases thus yielding very low throughput in congested areas. RTS/CTS access provides higher throughput but it applies only to unicast transmissions. To overcome the limitations of 802.11 protocols, we designed a protocol known as SOFT MAC which combines Space, Orthogonal Frequency and Time multiple access techniques. In SOFT MAC the road is divided into cells and each cell is allocated a unique group of subcarriers. Within a cell, nodes share the available subcarriers using a combination of TDMA and CSMA. The throughput analysis of SOFT MAC showed it has superior throughput compared to the basic access and similar to the RTS/CTS access of 802.11

Dual polarized modulation and reception for next generation mobile satellite communications

This paper presents the novel application of polarized modulation (PMod) for increasing the throughput in mobile satellite transmissions. One of the major drawbacks in mobile satellite communications is the fact that the power budget is often restrictive, making it unaffordable to improve the spectral efficiency without an increment of transmitted power. By using dual polarized antennas in the transmitter and receiver, the PMod technique achieves an improvement in throughput of up to 100% with respect to existing deployments, with an increase of less than 1 dB at low Eb/N0 regime. Additionally, the proposed scheme implies minimum hardware modifications with respect to the existing dual polarized systems and does not require additional channel state information at the transmitter; thus it can be used in current deployments. Demodulation (i.e., detection and decoding) alternatives, with different processing complexity and performance, are studied. The results are validated in a typical mobile interactive scenario, the newest version of TS 102 744 standard [Broadband Global Area Network (BGAN)], which aims to provide interactive mobile satellite communications.Peer ReviewedPostprint (author's final draft

Performance Evaluation of Vertical Bell Labs Layered Space Time (Vblast) Algorithms For Mimo System

In this paper a possible way of MIMO technique is used to exploit the multipath scattering properly, it is the Spatial Multiplexing, where the parallel streams of data are mixed up in the air but can be recovered at the receiver by using different Vertical Bell Labs Layered Space- Time (VBLAST algorithms like, Zero Forcing (ZF), Minimum Mean Square Error (MMSE), and QR-decomposition decoding methods. This paper focused in performance evaluation between these different algorithms in terms of Bit Error Rate (BER) performance using different modulation schemes (4PSK, 8PSK, 16PSK, and 16QAM), and different numbers of antennas. The results derived have shown that 4PSK has the best performance and 16PSK has the worst for all different types of receiver algorithms, with 16QAM constellation performance better than 16PSK, although they use the same bit rate. The BER performance degrades when the constellation size increases. Also the VBLAST receivers with VBLASTMMSE perform better than VBLAST-ZF and VBLAST-QR receiver in terms of BER when 2X2 antennas are used. Also, it is noted that with increasing modulation constellation the curves of BER are shifted to right due to the higher data rate that is transmitted. MMSE loses the advantage over ZF that is observed for lower constellations, and VBLAST-QR performs better than lower constellations. Finally it is noticed that the BER performance degrades with increasing the number of antennas