3GPP Long Term Evolution (LTE) and its enhancement has become the main candidate of 4G standards. Due to the requirements on high data rate and low latency for broadband wireless communication systems, LTE air-interface protocol stack must be designed and implemented with high data processing efficiency. Following a general description of the LTE user equipment (TIE), this paper analyzes the main challenges in the link-layer protocol stack design and implementation, including the data processing efficiency, synchronization, flexibility and portability. A reference design of LTE TIE link-layer protocol stack software is then presented with several design methodologies. A memory access optimization and light-weighted thread model are proposed to improve the data processing efficiency, while a hardware triggered synchronization mechanism is exploited to maintain synchronous between the link-layer protocol stack and the physical layer. Finally, the platform flexibility and portability is achieved by employing interface abstraction and adapters. Extensive system level testing shows that the proposed LTE TIE protocol stack software achieves high data rate and low data processing latency in a hardware resource restricted platform, which can be further extended to commercial LTE TIE products.

Due to frequent handovers in broadband wireless communications in high-speed rail, communication interruption during handover could seriously degrade the experiences of passengers on the train. Aiming to reduce the interruption time, this paper proposes a seamless handover scheme based on a dual-layer and dual-link system architecture, where a Train Relay Station is employed to execute handover for all users in a train and two antennas are mounted at the front and rear of a train. In the proposed scheme, the front antenna executes handover while the rear antenna is still communicating with BS, so that the communication can keep non-interruptive throughout the handover. Moreover, bi-casting is adopted to eliminate the data forwarding delay between the serving BS and target BS. A complete handover protocol is designed and the performance of the proposed scheme is analyzed. It can be seen from analytical results that the handover failure probability decreases as cell overlap increases and the communication interruption probability decreases with the decrease of train handover location and the increase of cell overlap. The simulation results show that in the proposed scheme, the communication interruption probability is smaller than 1% when the handover location is properly selected and the system throughput is not affected by handover. In conclusion, both theoretical and simulation results show that the proposed scheme can efficiently perform seamless handover for high-speed rail with low implementation overhead.

It is a great challenge to design an efficient handover scheme of broadband wireless communication systems for high-speed rail to reduce the communication interruption time during handover. A seamless handover scheme based on the dual-layer and dual-link system architecture is proposed in this paper. In the scheme, two antennas are mounted at the front and rear of a train, and one of them executes handover while the other is still communicating with BS. Therefore, the communication will not be interrupted throughout the handover. Furthermore, bi-casting is adopted to eliminate the data forwarding delay between the serving BS and target BS. In order to reduce handover implementation overhead, a Train Relay Station is employed to represent all the users in a train to execute handover in the proposed scheme. The performance of the proposed scheme is analyzed in terms of handover probability, handover failure probability and communication interruption probability. Simulation and theoretical results show that the proposed scheme can efficiently support seamless handover for high-speed trains with low implementation overhead.

In this paper, a novel call admission control (CAC) scheme for multicast and unicast integrated services is proposed, which optimizes service provision capacity for both services. A resource sharing model is presented in which multiple classes services are dynamically admitted into the system. Several basic CAC rules for the above resource model are proposed first and improved mechanisms are investigated to further increase system performance. Subsequently, the call level QoS and system performance of the resulting CAC scheme are evaluated. Numeric results show that the proposed scheme can achieve optimal multiclass service performance while satisfying QoS constraints.

In this paper, a novel radio admission control (RAC) scheme is proposed for handling multiclass services in Long Term Evolution (LTE) systems. An objective function of maximizing the number of admitted users is proposed to evaluate the system capacity. To solve the optimization problem, we present a combined complete sharing (CS) and virtual partitioning (VP) resource allocation model and develop a service degradation scheme in case of resource limitations in the proposed RAC scheme. Call blocking probability, system resource utilization and system capacity are used as performance metrics and are evaluated by using a K-dimensional Markov Chain model. Numerical results show that an optimal proportion of resource deployment for different service groups can be identified to maximize system capacity while at the same time maintaining quality of service (QoS) constraints of all admitted users.

In order to improve the efficiency of paging management, various paging strategies have been proposed for tracking single mobile user in the wireless cellular network. However, most of the schemes have ignored the important problem of efficient search for multiple mobile users under delay and bandwidth constraints. Given the condition that the search is over only after all the users in the group are found, this problem is defined as the Conference Call Search (CCS) problem. As opposed to the single user tracking, for which one can always reduce the expected search cost, for a multicast search the dependency between the delay and the search cost is NP-hard. In this paper, we propose a non-optimal search method that yields a low search delay as well as a low search cost. The 2D Markov walk is used as the mobility model which describes a broad class of mobility patterns. The Weighted Bipartite Graph Matching is used to allocate paging bandwidth which keeps a total maximum location probability at each paging round. Experimental results show that our paging scheme also achieves a low paging cost and delay compared to other schemes proposed in the literature.

In multiuser MIMO systems, the achievable system data rate as well as quality of service (QoS) of individual users is limited by the inter-user interference (IUI). The interference balancing issue via power allocation can be usually formulated as a nonconvex optimization problem which will become more intractable with nonconvex QoS constraints. In this paper we focus on the challenging QoS-aware optimal power allocation problem, aiming to maximize the system sum rate and guarantee the users' minimum data rates. As a result, a "Polynomial Approximations based on Single Condensation" (PASC) strategy is proposed which transforms the underlying problem to a series of tractable Geometric Programming (GP) problems through single condensation scheme. Extensive simulations have been conducted and the results indicate that PASC is quite suitable to tackle the problem, which can achieve a good balance between the system sum rate and the individual QoS requirements.

Various paging strategies have been proposed to improve the efficiency of paging management. However, most of the schemes ignore how to obtain location predictions or are too complex for real systems. In this paper, we propose a new adaptive paging scheme designed according to the mobility pattern and location probabilities. The Bayesian network is used as the location prediction model which describes a broad class of mobility patterns. The probability distribution of a mobile terminal's location is derived on the condition that the incoming calls form a Poisson process and the cell holding time has an exponential probability distribution. The paging strategy is implemented using a heuristic algorithm which can adaptively change according to the given mobility pattern and traffic parameters. The running time of the strategy is only ¿(N) where N describes the number of cells in a Tracking Area. Experimental results show that the adaptive paging scheme also achieves a low paging cost compared to other schemes proposed in the literature.

The concept of Logical Service Provision Number (LSPN) is proposed to evaluate the service provision capacity in multicast and unicast integrated multiclass service cellular networks. The tradeoff between call blocking probability and LSPN is investigated and an objective function of maximizing LSPN is proposed. To solve the optimal problem, the system is modeled as a 2K-dimensional Markov process with following features. The multiclass service system can provide multiple service classes using either multicast traffic or unicast traffic and each service class has call level QoS requirements. A static channel allocation model is adopted as the multicast traffic integration scheme. By solving the objective function, an optimal proportion of multicast traffic to unicast traffic can be identified to maximize the service provision capacity while satisfying QoS constraints.