Amoakoh Gyasi-Agyei

Survey of Wireless Communications Applications in the Railway Industry

Advances in information and communications technology have enabled the adoption of wireless communication techniques in all sectors for the transmission of information in all forms between any two points. Wireless communications and distributed computing have promoted the development of vehicle- monitoring systems to reduce the maintenance and inspection requirements of railway systems while maintaining safety and reliability. This paper surveys existing wireless techniques used in the railway industry for both communications and signalling purposes. Finally we present our work in progress on low-cost, low-power wireless sensor networking architecture to monitor the health of railway wagons attached to a moving locomotive.

Multiuser diversity based opportunistic scheduling for wireless data networks

Opportunistic scheduling (OS) is a modern view of communication over fading wireless channels, whereby, unlike rate adaptation based schemes, channel variations are exploited rather than mitigated. This letter proposes an OS scheme with embedded traffic parameters to provide fairness and differentiated QoS to different traffic types. Numerical investigations over Rayleigh fading channels show the throughput superiority of the scheme over round-robin policy while guaranteeing weighted fairness among different traffic classes.

Cross-layer multiservice opportunistic scheduling for wireless networks

We consider opportunistic communication in multiservice wireless data networks using centralized controllers. Opportunistic scheduling (OS) is an emerging cross-layer media access control design approach to multiuser communication over fading wireless channels. OS exploits channel variations to maximize wireless throughput. We present a general background of OS schemes and then propose an OS scheme making an optimum trade-off between throughput and fairness, while maintaining stability in different channel environments and guaranteeing minimum service to multiple queues active concurrently at a given user

Comparison of opportunistic scheduling policies in time-slotted AMC wireless networks

We consider scheduling schemes which exploit the random variability in wireless channels to maximize wireless throughput. We survey ten of such opportunistic scheduling policies, namely, PFS, OCASD, TAOS-1, I-OCASD, CASTI, EXP, M-LWDF, FIFO, RR and MaxC/I and compare them in terms of system throughput, fairness (user isolation) and the distributions of user starvation periods (packet delays) in a time-slotted wireless network like CDMA/HDR using adaptive modulation and coding (AMC). The results aids in determining the suitability of any of the ten policies in a wireless network depending on which metric is considered critical.

A Survey of Energy-Efficient and QoS-Aware Routing Protocols for Wireless Sensor Networks

Recent developments in wireless communications have enabled the development of low-cost, low-power wireless sensor networks (WSN) with wide applicability, including environment and vehicle-health monitoring. Minimizing energy consumption and hence maximizing the life time of the network are key requirements in the design of optimum sensor networking protocols and algorithms. Several routing protocols with different objectives have already been proposed for energy-efficient WSN applications. This paper surveys a sample of existing energy-efficient cluster-based and QoS-aware routing protocols and highlights their key features, including strengths and weaknesses

Performance of STT-Vegas in heterogeneous wired and wireless networks

TCP Vegas is a proactive congestion control mechanism proposed to improve TCP performance by using Round Trip Time (RTT) as a main parameter to monitor traffic condition and avoid congestion. However, TCP Vegas does not perform well on bidirectional links with unbalanced traffic, and on wireless links. A simple Single-Trip Time (STT) based modification to TCP Vegas, namely STT-Vegas, was introduced in [1] to improve the performance of TCP Vegas. It has been demonstrated that STT-Vegas outperforms Vegas in various network scenarios in wireline networks. This paper examines the performance of STT-Vegas in heterogeneous wired and wireless networks and investigates its possible enhancements in such networks.

Range Extension and Channel Capacity Increase in Direct Short Range Vehicular UWB Communications

Direct short range broadband communication access in vehicles promises to deliver high quality of service IP-based communications with networks deployed in moving vehicles. This paper provides an analysis of range extension and channel capacity increase in such networks when multi-hop communication is adopted for ultra wideband (UWB) communications. Received signal to noise ratio is used with multi-hopping to analyse range extension. Since the received signal levels for each short hop is higher compared with longer hops, the Shannon channel capacity for the short hops are equally higher leading to increased total channel capacity in multi-hop situations. Therefore cheaper and low powered transmitters can be used in the multi-hop scenario. The smaller transceivers also produce less interferences compared to the larger transceivers although it remains to be demonstrated if the total sum of the interference generated by the smaller transmitters is of the same order as that generated by the fewer but bigger transceivers.

Cross-Layer Scheduling of QoS-Aware Multiservice Users in OFDM-Based Wireless Networks

Constraint scheduling is a dynamic process of arbitrating between competing users sharing a finite resource. Cross-layer scheduling allows vertical interactions between some protocol layers to optimize system performance. This article proposes a cross-layer scheduling for orthogonal frequency-division multiplexing (OFDM) based wireless networks. The scheduler combines opportunistic communications and link adaptation to serve users with multiple concurrent flows (applications) of different quality of service (QoS) requirements. For each time slot and on each OFDM subcarrier, the scheduler computes a cost function for each flow that depends on a flow’s instantaneous link quality and service history. The flow with the least cost on an OFDM subcarrier is assigned the subcarrier, provided no other flow’s delay constraint is in violation. The scheme is scalable, optimizes wireless throughput, traffic delay-aware, guarantees minimum service to all active flows, and has low implementation complexity.