Research On Medium Access Control Scheme Of Cognitive Wireless Networking

MAC layer plays an important role in vertical handovers when roaming about heterogeneous wireless network. Therefore, it's necessary to investigate deeply on MAC layer's information and processed model to meet users'QoS requirements, including media independent network resource model, network information sensing model and link trigger handover decision scheme.But there are three main problems need to be improved. Firstly, each network performs resource allocation according to various techniques. There exists no such a unified metric for comparison the resources of different access schemes. Secondly, network information sensing model doesn't satisfy the requirements of vertical handover. Finally, the link trigger scheme didn't take moving state into account.This paper analyzed and investigated on these problems mentioned above, and then proposes network resource model which is applicable for Carrier Sense Multiple Access network and multi-rate allocation networks, a distribution information sensing model is brought forward for handover selection, and a moving-state based LGD link trigger scheme is proposed in order to enhance handover performance. The main contribution of the thesis as follows.1. According to the differences of heterogeneity in resource allocation, this paper employs the cube structure for establishing CSMA and multi-rate network resource, and then compares the cube model with standard method used in math.2. Two distributed MAC layer information sensing schemes are proposed for forced vertical handover and unforced vertical handover. Probability Information Sensing Model (PISM) and Broadcast Information Sensing Model (BISM), PISM applies the history serving information and MAC layer hands probability over high layer; BISM ,that is, parameters are obtained though sending request to AP/BS in network providing state information, and in CSMA network, we can derivate bandwidth and access delay via NAV vector. Energy saving is very important for multi-mode terminal, the sensing frequency is determined based on signal strength and network performance, which can significantly minimum the activating state time.3. This thesis proposes a terminal moving state-based LGD trigger handover algorithm. First, this scheme chooses Gauss-Markov entity moving model, then the distance between terminal and AP/BS can be derived though moving model, the signal strength is gained by employing Fritz path loss model. Weighted and sum the signal based on moving model and LMS predictive one, a new signal changing curve is described. This method is putting the signal strength as the foreknow information for LMS predictive scheme, and then predict the signal strength in the future. The LGD trigger proposed in this paper can be early fired in order to depress packet lose and idle time between handover finished and the real link down.