A. Lo

Cell switching mechanisms for access point sharing in WLAN over radio-over-fiber systems

Radio-over-fiber (RoF) technology is a promising candidate to provide high data rates and ubiquitous coverage by distributing small cells over the service area. For wireless LAN (WLAN) application in RoF systems, an access points (AP) can be shared among multiple small cells. The medium access mechanisms in the distributed coordination function (DCF) under this context encounter some issues due to the carrier sensing failure between the nodes in different cells. For alleviating this problem and also supporting flexible AP sharing, two switching mechanisms are discussed. One employs a time division scheme for sharing the APs and the other a selective reception of uplink frames among the associated cells. Both approaches are shown to be effective. The proposed mechanisms do not require changes in the existing protocols on both the client side and AP side. And they are complementary to each other due to their different switching principles.

Architectural and QoS Aspects of Personal Networks

Personal networks (PNs) are future communication systems that combine wireless and infrastructure based networks to provide users a variety of services anywhere and anytime. PNs introduce new design challenges due to the heterogeneity of the involved technologies, the need for self-organization, the dynamics of the PN composition, the application-driven nature, the co-operation with infrastructure-based networks, and the security hazards. This paper discusses the challenges of security, service discovery and QoS provisioning in designing self-organized PNs and combines them all into an integrated architectural framework

Coalition game-theory-based congestion control in Hybrid Fi-Wi indoor network

As more bandwidth hogging applications like video streaming or video conferencing are entering the telecom market, indoor networks need to be more efficient, failure-resilient and flexible. WiFi have predominantly been the most ubiquitous indoor wireless technology. WiFi Access Points (APs) are placed progressively in indoor locations resulting in highly congested ISM spectrum bands. Thus users are experience diminishing data rates. Hybrid Fiber-Wireless (Fi-Wi) architecture are pursued as the way forward for such large indoor networks. Fi-Wi provides a future proof backbone for supporting multiple wireless technologies indoor via a centralized controlled architecture. A residential gateway namely Home Communication Controller (HCC) hosts all APs and serve as the brain of the indoor network. Cell Access Nodes (CANs) located inside each room distributes the radio signals and are connected to the HCC (i.e. APs) using different optical wavelengths. The flexibility of the architecture makes it possible to switch the connection of APs with a different set of CANs periodically in order to reduce the congestion level of the whole network. Game theory is regarded as a major mathematical tool in formulating such congestion control problems. In this work we formulate the problem of congestion control using coalition game theory and propose a centralized assignment algorithm to dynamically assign CANs to APs. We prove that the assignment algorithm terminates in a stable partition which attains optimal grand aggregate utility for the network. The simulation results project a maximum decrease of 45% congestion level with 200 non-uniformly distributed users in the network.

A throughput fair SLNR scheduling algorithm for hybrid Fi-Wi indoor downlink MU-MIMO

Indoor downlink communication contributes to a large part of the data traffic generated in todays world. Enormous high data rate supporting devices are entering todays market. They demand for high rate wireless indoor coverage for their uninterrupted service. The main challenge lies in working with the existing wireless technologies while providing a future proof centralized optical fiber indoor backhaul for efficient indoor coverage. Fiber to the room paradigm is gaining a lot of attention in this regard. For supporting high data rates indoor, multiuser MIMO (MU-MIMO) is definitely a prominent choice. While quality of service serves as the most attractive feature that should be ensured among the mobile terminals (MTs). In this work we propose a throughput fair successive signal to leakage and noise ratio (SLNR) precoding algorithm for such a fiber-wireless (Fi-Wi) MU-MIMO indoor. The network capacity and individual MT data rate for our proposed scheme are compared against the greedy SLNR scheme and a random selection based SLNR precoding scheme. The Jains fairness index value for our scheme is shown to achieve maximal fairness.

Multiuser — MIMO for capacity gain in Fi-Wi hybrid networks

Fiber to the Rooms paradigm is gaining a lot of attention recently. In this paradigm, the last mile wireless (viz., IEEE 802.11×) connectivity, backed by optical fiber infrastructure, supports uncompressed high data rate while rendering seamless mobility and higher frequency reuse. To provide cost effective solution, Access Points (AP) in each room are replaced by distributed antennas. A centralized home communication controller provides AP functionality. WiFi inherently suffers from the problem of hidden nodes (HN). This problem persists even in the Fiber-Wireless (Fi-Wi) hybrid world causing degradation of throughput. In this paper we propose a Multi-User Multiple Input Multiple Output (MU-MIMO) uplink technique using both spatial and optical wavelength multiplexing. This scheme can increase the data rate significantly through diversity gain or spatial multiplexing. The proposed scheme is compared against an eminent joint decoding technique called Successive Interference Cancellation (SIC) adapted for operability in Fi-Wi indoor environment. The main contribution is that we propose an unique MU-MIMO uplink technique for Fi-Wi Hybrid indoor environment which address the problem of HN. We evaluate the performance of our proposed MU-MIMO technique based on ergodic capacity and probability of bit error.

Architectures for Communication in Personal Networks

Personal networks (PN) is a new concept related to pervasive computing with a strong user-focus view. The key to a successful PN realization is a general network architecture that is capable of bridging different current and future technologies and offers a homogeneous and clear view to the end-user. In this paper, we focus on forming a PN by connecting remote personal devices using infrastructure-based IP networks, including 3G networks and WLAN hotspots. One way is to upgrade the current access networks with new functionality to support PNs. Since many devices in PNs are mobile and battery powered, this may help them to achieve a faster service and to save energy. However, to deploy such functionality is not easy and may hamper the adoption of PNs altogether. Therefore, in this paper we study three possible inter-cluster communication architectures that can use current IP networks. To discern the above proposal we also give a detailed picture of PN network architecture supported by infrastructure. We believe that this detailed discussion will help the success of PNs

Effects of imperfect CSIT on downlink MU-MIMO fair SLNR scheduling algorithm

Indoor downlink communication contributes to a large part of the data traffic generated in todays world. The demand for high rate wireless indoor coverage while providing complete support to the existing wireless technologies is a big challenge. The future proof centralized optical fiber indoor back haul for efficient indoor coverage is gaining a lot of attention recently. Physical layer techniques like multiuser MIMO (MU-MIMO) is becoming an inevitable approach in this regard. Quality of service serves as the most attractive feature that should be ensured among the mobile terminals (MTs). In this work we try to study the effects of imperfections in channel knowledge owing to estimation errors. We study the effects of it on our previously proposed throughput fair successive signal to leakage and noise ratio (SLNR) precoding algorithm [1] for such a fiber-wireless (Fi-Wi) MU-MIMO indoor. Our algorithm has been shown previously to achieve maximal fairness. In this paper we use MMSE alterations to significantly reduce the effect of estimation errors for our scheme. We provide a lower bound on the sum rate achievable with imperfect CSIT. In this paper we also compare different power allocation policies. Power allocation policies plays an important part in improving the performance of the system in terms of BER of the worst case user. We show that channel adaptive power allocation guarantees approximately 3dB SNR improvement over the equal power allocation policy for BER of 10-7.

Successive interference cancellation in the uplink of Radio-over-Fiber systems

Successive Interference Cancellation (SIC) is a well-known technique for enhancing wireless channel efficiency by allowing concurrent transmissions from multiple users. This multiuser detection technique is usually used in cellular systems. In this paper we adapt it to Radio-over-Fiber (RoF) system for the same purpose. Due to the similarity to using SIC in typical cellular networks, we mainly focus on exploring the uniqueness of applying SIC in a distributed antenna application of RoF for uplink communication. We find that the physical channel capacity is decreased by additional noise in distributed antennas, but the MAC layer throughput could still be increased due to simultaneous transmission. We show that the performance can be further improved by employing transmit power control at the terminals and amplification control at the remote access units. All these findings make us believe that SIC is a promising technique in RoF system.