In recent communications systems, various kinds of traffic are transmitted all together. The mixed delay and non-delay system, which integrates loss-sensitive delay (data) traffic and delay-sensitive realtime (voice) traffic, is a typical example of these systems. In the mixed delay and non-delay systems, the non-delay traffic generally suffers loss with a relatively large probability due to the existence of the delay traffic. In order to improve the GOS (Grade of Service) of the non-delay traffic and to increase the efficiency of the overall systems, the alternative routing scheme is introduced. In design of the alternative routing systems, analysis of overflow traffic essential. This paper focuses on the moments of the number of the overflow calls from the mixed delay and non-delay systems with Poisson inputs and exponential service times. In the case of same mean service time, explicit formulas are presented for the moments, whereas a recursion formula and its calculating algorithm are derived in the case of different mean service times. Through the numerical results, a limiting property of the moments is discussed. An example is given to show the application of the obtained formulas.

This paper presents a mobility management scheme that combines host-based routing (HBR) with prefix routing to achieve balanced loading of network nodes in a distributed hierarchically arranged mobile IPv6 access network. This allows the higher-level nodes to be less loaded than in pure host based routing schemes, where the root node presents a capacity bottleneck to the system. As a result, this scheme achieves good savings in memory by reducing host-specific caches, and thus enhances network scalability. A direct consequence of reduced database entry is reduced processing latencies at the nodes, which reduces delay and improves on network performance. Our hybrid HBR scheme performs better than the pure HBR schemes in memory conservation and increased network capacity.

Channel state information (CSI) at transmitter plays an important role for multiuser MIMO broadcast channels, but full CSI at transmitter is not available for many practical systems. Previous work has proposed orthonormal random beamforming (ORBF) [16] for MIMO broadcast channels with partial channel state information (CSI) feedback, and shown that ORBF achieves the optimal sum-rate capacity for a large number of users. However, for cellular systems with moderate number of users, i.e., no more than 64, ORBF only achieves slight performance gain. Therefore, we analyze the performance of ORBF with moderate number of users and total transmit power constraint and show that ORBF scheme is more efficient under low SNR. Then we propose an adaptive ORBF scheme that selects the number of random beams for simultaneous transmission according to the average signal-to-noise ratio (SNR). Moreover, a multi-beam selection (MBS) scheme that jointly selects the number and the subset of the multiple beams is proposed to further improve the system performance for low SNR cases. The simulation results show that the proposed schemes achieve significant performance improvement when the number of users is moderate.

The existing carrier sensing multiple access (CSMA) based wireless networks cannot realize the capture effect functionality. Consequently, transmitters within the physical carrier sensing (PCS) range of a receiver cause interference to its reception, which is referred to as the pseudo capture effect. Such interference severely degrades the system performance because the default PCS range is usually quite large. Therefore the PCS range should be adjusted to reduce the packet loss caused by pseudo capture effect. In order to guide the optimal PCS range setting, a modified p-persistent model is proposed in this paper to investigate the throughput of CSMA-based networks considering pseudo capture effect. Simulation results show that the proposed model accurately evaluates the influence of pseudo capture effect. By utilizing the model, we observe that the optimal PCS range considering pseudo capture effect is smaller than the case without considering its impact.

In this paper, we investigate the proportional fair scheduling (PFS) problem for multiuser OFDM systems, considering the impact of packet length. Packet length influences scheduling schemes in a way that each scheduled packet should be ensured to be completely transmitted within the scheduled frames. We formulate the PFS problem as an optimization problem. Based on the observations on the structure of optimal solutions, we propose a heuristic scheduling algorithm that consists of two stages. First, subcarriers are allocated among users without considering the packet length constraint. Then on the second stage, subcarrier readjustment is done in a way that surplus subcarriers from length-satisfied users are released and allocated among length-unsatisfied users. The objective is to provide proportional fairness among users while guaranteeing complete transmission of each scheduled packet. Simulation results show that the proposed scheme has quite close performance to the optimal scheme in terms of Multi-carrier Proportional Fairness Measure (MCPFM), throughput and average packet delay.

This paper proposes an adaptive transmission scheme for MIMO systems to provide different bit error rates and transmission rates for multimedia traffic. The adaptive transmission scheme allocates antennas, rate and power jointly according to the feedback information to satisfy the diverse QoS requirements of the multimedia traffic. Furthermore, an efficient search algorithm with low complexity is proposed for practical implementation. Simulation results show that the proposed scheme improves the spectral efficiency while guaranteeing the QoS requirements of multimedia traffic. Moreover, the proposed search algorithm achieves close optimal performance with great complexity reduction.

For coherent detection, decoding Orthogonal Space-Time Block Codes (OSTBC) requires full channel state information at the receiver, which basically is obtained by channel estimation. However, in practical systems, channel estimation errors are inevitable and may degrade the system performance more as the number of antennas increases. This letter shows that, using fewer receive antennas can enhance the performance of OSTBC systems in presence of channel estimation errors. Furthermore, a novel adaptive receive antenna selection scheme, which adaptively adjusts the number of receive antennas, is proposed. Performance evaluation and numerical examples show that the proposed scheme improves the performance obviously.

The performance of multiuser MIMO downlink systems with block diagonalization (BD) relies on the channel state information (CSI) at the transmitter to a great extent. For time division duplex TDD systems, the transmitter estimates the CSI while receiving data at current time slot and then uses the CSI to transmit at the next time slot. When the wireless channel is time-varying, the CSI for transmission is imperfect due to the time delay between the estimation of the channel and the transmission of the data and severely degrades the system performance. In this paper, we propose a linear method to suppress the interferences among users and data streams caused by imperfect CSI at transmitter. The transmitter first sends pilot signals through a linear spatial precoding matrix so as to make possible that the receiver can estimate CSI of other users, and then the receiver exploits a linear prefilter to suppress the interference. The numerical results show that the proposed schemes achieve obvious performance enhancement in comparison to the BD scheme with imperfect CSI at the transmitter.

A key problem under imperfect power control in multimedia DS-CDMA networks is how to guarantee the differentiated outage probabilities of different traffic classes resulted from the uncertainty of received powers. In addition, in order to utilize the scarce wireless resource efficiently, as many users as possible should be admitted into the network while providing guaranteed quality-of-service support for them. In this work, a call admission control scheme, Differentiated Outage Probabilities CAC or DOP-CAC, is proposed to achieve the above goals for imperfectly power-controlled multimedia CDMA networks. Two important features of CDMA systems are considered in our scheme: one is the power multiplexing among bursty traffics and the other is the power allocation scheme employed at the physical layer. The validity and efficiency of DOP-CAC are verified by numerical examples. Two power allocation schemes, Limited Optimal Power Allocation (LOPA) proposed in [3] and Quasi-Optimal Power Allocation (QOPA) we proposed in [6], are considered respectively and compared in the performance evaluation of DOP-CAC. The results show that DOP-CAC achieves much better resource utilization under QOPA than it does under LOPA. By employing QOPA at the physical layer and DOP-CAC at the link layer, our work suggests a high efficiency solution for QoS support of multimedia traffic under imperfect power control environment.

This paper addresses the utility-based radio resource allocation problem in DS-CDMA systems carrying multimedia traffic. The proposed scheme, aiming at achieving optimal resource allocation, considers the joint power and data rate allocation. To avoid high computational complexity of nonlinear optimization, we reformulate the radio resource allocation problem as a market model, where resource is regarded as a commodity. Since the market model satisfies the incentive-compatible constraint, the optimal resource allocation can be obtained at the market equilibrium in a distributed manner. According to whether to allocate a minimal transmission data rate to each user, two algorithms, UCA and FCA, are proposed. UCA emphasize on maximizing system overall utilities, while FCA guarantees fairness to users. Simulation results show that the proposed radio resource allocation scheme and algorithms are flexible and efficient for multimedia DS-CDMA systems.

With simultaneous multi-user transmissions, spatial division multiple access (SDMA) provides substantial throughput gain over the single user transmission. However, its implementation in WLANs with contention-based IEEE 802.11 MAC remains challenging. Problems such as coordinating and synchronizing the multiple users need to be solved in a distributed way. In this paper, we propose a distributed MAC protocol for WLANs with SDMA support. A dual-mode CTS responding mechanism is designed to accomplish the channel estimation and user synchronization required for SDMA. We analytically study the throughput performance of the proposed MAC, and dynamic parameter adjustment is designed to enhance the protocol efficiency. In addition, the proposed MAC protocol does not rely on specific physical layer realizations, and can work on legacy IEEE 802.11 equipment with slight software updates. Simulation results show that the proposed MAC outperforms IEEE 802.11 significantly, and that the dynamic parameter adjustment can effectively track the load variation in the network.

We study the influence of decoding order on the capacity of multimedia DS-CDMA system employing imperfect successive interference cancellation. We prove that the capacity is maximized by decoding users according to the ascending order of cancellation errors. We also prove that this capacity-optimal decoding order makes total residual interference minimum at the same time.

In wireless networks, sleep mode based power saving mechanisms can reduce the energy consumption at the expense of additional packet delay. This letter analyzes its packet queueing delay and wireless terminals' energy efficiency. Based on the analysis, optimal sleep window size can be derived to optimize terminal energy efficiency with delay constraint.

In contention-based wireless ad hoc networks, power control is an efficient way to improve the spatial reuse by allowing multiple pairs to communicate simultaneously. In this paper, we propose a game-theoretical approach for joint power and rate control in ad hoc networks, where the transmit rate of each link is maximized. Meanwhile we consider the transmit power as the cost, since higher power leads to higher interference and more energy consumption. In particular, we introduce a novel auction-like pricing algorithm in which the cost per unit power steps up until the network settles down at a Nash equilibrium, which is a feasible power and rate allocation, even when the Signal to Interference and Noise Ratio (SINR) requirements are initially infeasible. Numerical results show significant throughput improvement and energy consumption savings compared with the previously proposed algorithm that defers the link with minimum SINR.

In this letter, we propose a novel precoding scheme for base station (BS) cooperation in downlink cellular networks that allow overlapped clusters. The proposed precoding scheme is designed to mitigate the overlapping-BS interference by maximizing the so-called clustered virtual signal-to-interference-plus-noise ratio (CVSINR). Simulations show that with the proposed scheme, overlapped clustering provides substantial throughput gain over the traditional non-overlapped clustering methods, and user fairness is also improved.

In this paper, we develop a new distributed adaptive power control framework for multi-cell OFDM systems based on the game theory. A specific utility function is defined considering the users' achieved average utility per power, i.e., power unit based utility. We solve the subcarrier allocation issue naturally as well as the power control. Each user tries to maximize its utility by adjusting the transmit power on each subcarrier. A Nash equilibrium for the game is shown to exist and the numerical results show that our proposal outperforms the pure water-filling algorithm in terms of efficiency and fairness.

In wireless communication systems where users compete for limited bandwidth, radio resource control is essential for throughput enhancement and delay reduction. In this paper, we present a game-theoretical approach to distributed resource control in CDMA systems. Incomplete information about channel conditions is considered. The resource control problem is formulated as a noncooperative game of incomplete information, with which the existence and uniqueness of the Bayesian Nash equilibrium (BNE) of the game is investigated. Since the equilibrium is Pareto inefficient, we propose a pricing policy to the resource control game by adding a penalty price to user's transmission cost. With the adoption of the price, user's aggressive behavior is depressed, and Pareto improvement is achieved. Also the Pareto efficient BNE of the game with pricing is studied. Simulation results show that users can obtain higher throughput and lower average packet transmission delay by proper pricing policy. It is also verified that the scheme of pricing policy is robust when information of channel conditions is inaccurate.

In this work, we consider a remote estimation system where a remote controller estimates the status of heterogeneous sensing devices with the information delivered over wireless channels. Status of heterogeneous devices changes at different speeds. With limited wireless resources, estimating as accurately as possible requires careful design of status update schemes. Status update schemes can be divided into two classes: centralized and decentralized. In centralized schemes, a central scheduler coordinates devices to avoid potential collisions. However, in decentralized schemes where each device updates on its own, update decisions can be made by using the current status which is unavailable in centralized schemes. The relation between these two schemes under the heterogeneous devices case is unclear, and thus we study these two schemes in terms of the mean square error (MSE) of the estimation. For centralized schemes, since the scheduler does not have the current status of each device, we study policies where the scheduling decisions are based on age of information (AoI), which measures the staleness of the status information held in the controller. The optimal scheduling policy is provided, along with the corresponding MSE. For decentralized schemes, we consider deviation-based policies with which only devices with estimation deviations larger than prescribed thresholds may update, and the others stay idle. We derive an approximation of the minimum MSE under the deviation-based policies and show that it is e/3 of the minimum MSE under the AoI-based policies. Simulation results further show that the actual minimum MSEs of these two policies are even closer than that shown by the approximation, which indicates that the cost of collision in the deviation-based policy cancels out the gain from exploiting status deviations.

We propose a finite-capacity single-vacation model, with close-down/setup times and a Markovian arrival process (MAP), for SVC-based IP-over-ATM networks. This model considers the SVC processing overhead and the bursty nature of IP packet arrivals. Specifically, the setup time corresponds to the SVC setup time and the vacation time corresponds to the SVC release time, while the close-down time corresponds to the SVC timeout. The MAP is a versatile point process by which typical bursty arrival processes like the IPP (interrupted Poisson process) or the MMPP (Markov modulated Poisson process) is treated as a special case. The approach we take here is the supplementary variable technique. Compared with the embedded Markov chain approach, it is more straightforward to obtain the steady-state probabilities at an arbitrary instant and the practical performance measures such as packet loss probability, packet delay time, and SVC setup rate. For the purpose of optimal design of the SVC-based IP-over-ATM networks, we also propose and derive a new performance measure called the SVC utilization ratio. Numerical results show the sensitivity of these performance measures to the SVC timeout period as well as to the burstiness of the input process.

In this paper, we propose a polling-based scheduling strategy for multiple access control in wireless ATM networks (POSTMAN). A pure centrally controlled polling scheme is adopted in our protocol, therefore no contention channel is needed. The POSTMAN protocol assumes a TDMA/TDD frame format, by which wireless bandwidth is allocated flexibly both among multiple mobile terminals and between downlink and uplink channels. When polling the uplink traffic, the POSTMAN needs no priori traffic model to predict the cell arrivals. Instead, a token queue and an ABR buffer status table are used in the base station. Simulation results show that the POSTMAN protocol is robust in most cases and can work steadily under very high network load conditions.