It is a common problem for Wireless LAN (WLAN) users when they face more than one available Access Point (AP): which one may serve them better? In the real world, most WLAN devices and users select the AP by Received Signal Strength (RSS), which doesn't consider the load of APs. Therefore, the RSS-based scheme may result in load imbalance and utilization degradation. This paper proposes a simple scheme to inform WLAN users the available bandwidth when selecting a specific AP. Unlike the previous work, the new scheme concerns about the aggregated traffic patterns in AP, which affects the amount of the available bandwidth. Considering the number of active stations and influence of collision, the available bandwidth is calculated and regarded as a selection metric. Common users can acquire this metric through Service Set IDentifier (SSID) without any modifications on their devices, and users who accept modifications can select the preferable AP dynamically and automatically. This scheme is very simple to be implemented and deployed with negligible overhead to network. We conduct simulations to verify this scheme, which can improve by 200% the user's throughput in some situations.

In this paper, we investigate the Frequency Domain Packet Scheduling (FDPS) problem for 3GPP Long Term Evolution (LTE) Uplink (UL). Instead of studying a specific scheduling policy, we provide a unified approach to tackle this issue. First, we formalize a general LTE UL FDPS problem, which is suitable for various scheduling policies. Then, we prove that the problem is MAX SNP-hard, which implies that approximation algorithms with constant approximation ratios are the best that we can hope for. Therefore, we design two approximation algorithms, both of which have polynomial runtime. The first algorithm is based on a simple greedy method. The second one is based on the Local Ratio (L-R) technique and it can approximately solve the LTE UL FDPS problem with an approximation ratio of 2. To further analyze the stability of the 2-approximation L-R algorithm, we derive a specific FDPS problem, which incorporates the queue length and channel quality information. We utilize the Lyapunov Drift to prove the L-R algorithm is stable for any $((\omega_0, \epsilon_0))$-admissible LTE UL systems. The simulation results indicate good performance of the L-R scheduler.

Wireless Sensor Networks (WSNs) are embracing an increasing number of real-time applications subject to strict delay constraints. Utilizing the methodology of potential field in physics, in this article we effectively address the challenges of real-time routing in WSNs. In particular, based on a virtual composite potential field, we propose the Potential-based Real-Time Routing (PRTR) protocol that supports real-time routing using multipath transmission. PRTR minimizes delay for real-time traffic and alleviates possible congestions simultaneously. Since the delay bounds of real-time flows are extremely important, the end-to-end delay bound for a single flow is derived based on the Network Calculus theory. The simulation results show that PRTR minimizes the end-to-end delay for real-time routing, and also guarantees a tight bound on the delay.

In this paper, we formalize a general Frequency Domain Packet Scheduling (FDPS) problem for 3GPP LTE Downlink (DL). The DL FDPS problem incorporates the SingleUser Multiple Input Multiple Output (SU-MIMO) technique, and can express various scheduling policies, including the Proportional-Fair metric, the MaxWeight scheduling, etc. For LTE DL SU-MIMO, the constraint of selecting only one MIMO mode (transmit diversity or spatial multiplexing) per user in each transmission time interval (TTI) increases the hardness of the FDPS problem. We prove the problem is MAX SNP-hard, which implies approximation algorithms with constant approximation ratios are the best we can expect. Subsequently, we propose an approximation algorithm of polynomial runtime. The solution is based on a greedy method for maximizing a non-decreasing submodular function over a matroid. The algorithm can solve the general DL FDPS problem with an approximation ratio of 4. We implement the proposed algorithm and compare its performance with other well-known schedulers.

This paper investigates the interactions between two-way TCP connections over 3GPP LTE networks. In the LTE network, the two-way TCP flows share buffers on a common bottleneck, i.e., the radio access links. The behaviors of TCPs significantly influence the others in the opposite direction. Specifically, the radio links of LTE are asymmetric, which may induce drastic interactions of TCPs and rapid draining of downlink buffer. The periodic idleness of downlink is a huge waste of the precious radio bandwidth and results in considerable performance degradation. In the viewpoint of Coupled Queues, we thoroughly understand the interacting TCPs and explain the reason for performance degradation. Based on a straightforward modeling procedure, we formalize the evolution of two-way TCPs and model the bottleneck queue size in every slot. The model indicates the queues are close coupled, which is verified with simulations on NS2. If the uplink (queue) is fully utilized, the downlink (queue) will always be underutilized even idle, and vice versa. Furthermore, an effective solution called Preemptive ACK Queueing (PAQ) is designed to decouple the queues, which improves the performance of two-way TCPs over LTE networks.

The Wireless Sensor Network (WSN) is embracing an increasing number of real-time applications subject to strict delay constraints. Utilizing the methodology of potential field in physics, we present an effective way to address the challenges in real-time transmission. We propose the Potential based Real-Time Routing (PRTR) protocol, which provides real-time transmission using multi-path routing algorithm based on a composite potential field. PRTR features a delay-minimized real-time routing as well as alleviating congestion simultaneously.