D Diptanil Debbarma

Measurements and performance of large MIMO systems at 2.4 GHz for indoor WLAN

Large MIMO is a new and promising technique for boosting wireless link capacity. Currently, the research of large MIMO focuses on the theoretical aspects while work on the practical implementations and analysis are very limited. In this paper, we present some critical investigations on the behaviors of large MIMO in real propagation environment based on extensive channel measurements. On the one hand, our analysis has verified the advantages that the MIMO channel vectors between users tend to be orthogonal and the optimal capacity approximates the theoretical upper bound as the antenna array size grows. On the other hand, we observe that the practical limitations of allowable antenna array size and achievable spatial degrees of freedom in the physical channel have significant impacts. Furthermore, in order to enable the utilization of linear precoding techniques in such high-dimensional MIMO systems to achieve close-to-optimal capacity, a large ratio between the antenna array size of the large MIMO system and the number of simultaneously served users should be maintained.

Green hybrid Fi-Wi LAN

Enterprise WLANs encompassing supernumerary Access Points (APs) are being used to provide capacity to indoor environments. The approach of over dimensioned deployment of APs to meet the capacity needs of users at critical time points are advocated without little concern towards the important issue of power wastage. For a sustainable greener environment the issue of power saving in such enterprise WLANs has to be integrated in our present day design. Hybrid Fiber-Wireless (Fi-Wi) LAN is envisioned as the evolution of enterprise WLAN which can help us enormously to reduce the power wastage while meeting the demands of the indoor users. In this paper, we propose a hybrid Fi-Wi LAN architecture based On Demand Strategy which results in massive power saving (approximately 60%) by switching of APs or Cell Access Nodes (CANs) based on user demand estimation while maintaining coverage throughout the whole cell area.

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.

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.

Reduction of downlink delay time for heterogeneous users in Fi-Wi indoor networks

Ubiquitous presence of umpteen WiFi access points (AP) in indoor locations leads to massive degradation in effective data rates acquired by users. Indoor space contributes approximately 80% [1] of the data generated in todays world. Thus, radio resource management in indoor environment calls for immediate attention. Hybrid Fibre-Wireless (Fi-Wi) architecture for indoor has been proposed to combine the benefits of a huge bandwidth availability of fibre with the mobility offered by wireless access. In this paper, we propose a managed hybrid Fi-Wi indoor network. It consists of fibre infrastructure emanating from central home communication controller. Radio-over-fibre technology is used to distribute the radio signals throughout the indoor space using cell access nodes (CANs) to cover the immediate periphery inside rooms. The biggest advantage of such architecture is the ease of managing centrally the indoor radio resources for guaranteeing a better Quality of Service amongst heterogeneous user. In this paper, we model the problem of CAN to AP assignment based on downlink transmission delay experienced by users. We propose a centralised assignment method based on the reduction of overall network downlink transmission delay. Using MATLAB simulations, we show that a massive 66% reduction in the maximum downlink delay time for non-uniform distribution of heterogeneous users can be achieved. Finally, we prove the optimality of the centralised assignment algorithm using coalition game theory. Copyright

Sum-rates of radio-over-fiber small cell networks and massive MIMO for indoor communications

Small cell networks (SCN) and massive MIMO are both promising techniques for improving the network capacity. In this paper, we consider applying both concepts for indoor communications based on a radio-over-fiber (RoF) infrastructure. We give a comparison of the achievable sum-rates using the same system configurations which include the same set of active antennas and the same power constraints. The sum-rates are further optimized based on Geometric Programming, under both sum power constraint (SPC) and per antenna power constraint (PAPC). The numerical results indicates that both SCN and Massive MIMO offers a high network capacity. The capacity can be significantly increased when the number of antennas is a few times larger than the simultaneously served mobile stations (STAs). Massive MIMO performs much better provided that the inter-stream interference (ISI) can be canceled by the precoding techniques such as zero-forcing (ZF). However, with maximum ratio transmission (MRT), the performance of massive MIMO is poorer than SCN.

Feedback bit allocation for large distributed antenna systems in indoor WLAN

Massive MIMO is a key technique for next generation wireless networks due to its potential for significant capacity improvement. To achieve good performance, accurate channel state information (CSI) is needed, especially at the transmitter, to calculate the beamforming matrices. This problem exists for traditional MIMO systems and becomes more challenging for Massive MIMO as the number of antennas is much larger. In this paper, we focus on Massive MIMO with distributed antenna system (DAS) architecture, which we refer as large DAS. In a large DAS, a large number of remote antenna units (RAUs), each equipped with a small antenna array, are distributed over the service area, cooperatively working for beamforming. Due to the large separation of the RAUs, the large scale fading factors of the RAUs for a given mobile station (STA) is different. This effect can be utilized for optimizing the feedback bit allocation considering that more bits should be allocated to dominant signal paths. So we propose two bit allocation algorithms, one that adaptively allocates different bits to the RAUs according to the large scale fading, termed adaptive allocation; and the other that allocates equal bits to a set of RAUs, termed equal allocation. They are applied for centralized and de-centralized zero-forcing beamforming (C- and D-ZFBF) respectively. The results show that with a proper bit allocation, the data rates can approximate that of perfect CSI with limited feedback rate. For C-ZFBF, adaptive allocation performs better than equal allocation with medium feedback rates, and similarly for low and high feedback rates. For D-ZFBF, adaptive allocation and equal allocation offer similar results.

Energy efficient Fi-Wi LAN with performance optimization

In the IEEE 802.11 standard meager effort has been invested towards devising greener WLAN communication. Especially with the massive deployment of Enterprise WLAN in indoor networks a lot of access points (APs) are densely packed for increasing the capacity offered. But most of the APs deployed are idle for a larger period of time in a day. This paper proposes to use a centralized controlled distributed antenna systems employing Radio over Fiber (RoF) techniques for efficiently managing energy resources in the network. The main contribution of the paper is that we propose power managed load balanced (PMLB) algorithm which minimizes the total power consumption of the overall network while appeasing the user demand and also provides load balancing across the APs for a better network performance.