Notorious hidden and exposed terminal problems lead to severe unfair and inefficient utilization of the channel resource in wireless ad hoc networks and wireless LANs. The two problems are intrinsic in wireless networks, and have been troubling the research community for over a decade. Additionally, the sleep mode power saving mechanism has been a crucial issue in the design of future wireless networks as mobile stations (MSs) are powered by a battery with limited capacity. Exactly how the sleep mode operation affects the handover and the power saving efficiency of an MS in the inter-Base Station (inter-BS) movement has not been carefully investigated. This thesis focuses on addressing the aforementioned problems.

In the hidden terminal problem, we prove that the key assumptions...[ Read more ]

Notorious hidden and exposed terminal problems lead to severe unfair and inefficient utilization of the channel resource in wireless ad hoc networks and wireless LANs. The two problems are intrinsic in wireless networks, and have been troubling the research community for over a decade. Additionally, the sleep mode power saving mechanism has been a crucial issue in the design of future wireless networks as mobile stations (MSs) are powered by a battery with limited capacity. Exactly how the sleep mode operation affects the handover and the power saving efficiency of an MS in the inter-Base Station (inter-BS) movement has not been carefully investigated. This thesis focuses on addressing the aforementioned problems.

In the hidden terminal problem, we prove that the key assumptions of its causes that underlie previous studies are in fact incorrect, and further prove that the severity of hidden terminals is rate-dependent. This new insight leads to a simple and efficient rate-matching scheme for tackling the hidden terminal problem. In the exposed receiver problem, we propose a receiver assistance feature as an addition to the existing sender-initiated Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) protocol so that the exposed receiver can help its sender contend for channel access, which effectively improves the fairness of the disadvantaged link. The new addition maintains the simplicity and advantage of the sender-initiated MAC, while also leveraging the benefit from the receiver-initiated MAC to avoid the unfairness pitfall. We then address the exposed sender problem to enable more concurrent transmissions, which leads to a joint solution for both hidden and exposed terminal problems by leveraging the multi-rate properties and transmission power control. All the proposed schemes are either fully compatible with or can be easily embedded into the existing dominant IEEE 802.11 MAC. Extensive simulation results demonstrate that the proposed schemes achieve much better performance than that of the IEEE 802.11 MAC, the widely used benchmark for comparison.

Sleep mode power saving mechanisms introduced by IEEE 802.16e/m aim to save power. Existing studies on the sleep mode performance only assume the intra-Base Station (intra-BS) movement for an MS. How the sleep mode operation affects the handover and the power saving efficiency when the inter-Base Station (inter-BS) movement is frequent has not been carefully investigated. We develop an analytical model describing the operation of various versions of IEEE 802.16e/m sleep mode power saving mechanisms, and study their connection dropping probabilities and energy saving efficiencies. We show that existing sleep mode mechanisms do not work well and often lead to frequent connection drops and low power saving efficiency when mobility is high. Based on insights provided by the analytical model, we propose a handover scheme as an add-on to the existing sleep mode schemes to improve their performances in a high mobility environment. The simulation results show that the proposed scheme can effectively solve the connection dropping problem, and significantly improve the power saving efficiency even when inter-BS crossing is frequent.