Frank La Sita

Carrier Grade Wi-Fi: Air interface requirements and technologies

The IEEE 802.11 standardization group has recently ratified 802.11ac as the newest major amendment of the 802.11 family of Wi-Fi standards. While 802.11ac has specified a number of improvements over 802.11n such as: (i) 8 spatial streams (ii) mandatory bandwidth of 80 MHz and (iii) multi-user MIMO on the downlink, these improvements mostly target to improve the per-link throughput, and in case of MU-MIMO, traffic performance on the downlink. In order to satisfy the air interface high efficiency requirements and technologies, herein referred to broadly as 5G-Carrier Grade WiFi (5G-CGW), it is important to consider other metrics for system performance, such as area-throughput and Quality of Experience (QoE), which are more relevant in use cases where there can be a dense deployment of access points (APs), and stations (STAs). Recently, 802.11 started a study group called High Efficiency Wi-Fi (HEW) to develop the next generation of Wi-Fi physical (PHY) and medium access control (MAC) protocols that would satisfy these requirements. In this paper we will first provide an overview of the state-of-the-art in 802.11 standards, followed by a discussion on some of the limitations of 802.11ac in use cases of interest such as dense deployments in apartment buildings, stadiums and airports. We will provide an overview and preliminary simulation results of three technologies that have shown promise for meeting the requirements of CGW: (i) Multi-User Parallel Channel Access (MU-PCA) which would allow APs to simultaneously transmit to and to receive from a number of STAs in the frequency domain: enabled through multiplexing. This would alleviate the problem of underutilization of frequency resources caused by the need to support STAs of different bandwidths. (ii) Uplink Multi-User MIMO (UL MU-MIMO): IEEE 802.11ac standardized multi-user simultaneous transmissions in the downlink via downlink MU-MIMO. Uplink MU-MIMO needs to be defined to enable multiple users to share the spatial domain and transmit at the same time in the uplink. (iii) Fractional CSMA and Transmit Power Control (TPC): In a dense deployment of APs, the performance of overlapping basic service sets (BSSs) can be improved by coordinating the transmitted power in the adjacent APs in such a manner that STAs on the edge of coverage face reduced interference.

Carrier frequency offset correction for uplink multi-user MIMO for next generation Wi-Fi

In this paper, we study carrier frequency offset estimation and correction for uplink multi-user MIMO (UL MU-MIMO) for Wi-Fi, where distributed stations (STAs) send multiple data streams to a common access point (AP) with multiple receive antennas. We provide a description of the proposed system, and propose a three-step approach using a joint phase estimation algorithm for carrier frequency synchronization that takes advantage of the existing pilot signals to deliver good performance and also has low complexity. We provide simulation results to demonstrate that the proposed approach incurs negligible performance loss due to carrier frequency offsets.

Improved Spatial Reuse for Dense 802.11 WLANs

Next generation 802.11 networks aim to significantly increase spectral frequency reuse and manage interference between neighboring Overlapping Basic Service Sets (OBSS) in scenarios with a high density of both STAs and APs . In this paper, we study the theoretical throughput gains that may be obtained by using ideal spatial reuse in a densely occupied two-BSS network operating in saturated uplink traffic conditions (i.e. the transmission queue is never empty). We then compare the theoretical throughput gains with the gains obtained by implementing a practical spatial reuse technique in a residential scenario [6] using a discrete event simulator that integrates both the PHY and the MAC [7]. Our results show that the trends identified in the simple analysis are present in the empirical simulation and demonstrate that the gains obtained may depend on the scenario. We also conclude that additional spatial re-use techniques may be needed to extract all the gains promised by the theoretical analysis.