WiFi: What is phy restart? Why is it important in dense RF environments?

 Phy restart on radio drivers typically means if the hardware (radio) is able to sync to the preamble of a packet which has a stronger signal strength while it is already in the process of decoding a packet.

This is typically useful in noisy environments to achieve a "capture effect", where the stronger packet is finally decoded at the rx. radio. If the radio does not support PHY restart then typically such a reception would result in a collision on the rx-side at the radio.

WiFi: Load balancing through probe response control

Basic Idea:

Clients use probe requests as one of the first frames before connecting to an access point (AP). If the AP does not respond with a probe-response frame, the client will not proceed with the connection. We leverage this condition to control how clients are distributed across multiple access points in the network. This approach to client - balancing has the advantage that:

1. Load both RF and CPU are balanced across the APs.

2. No disconnect/connect is required for load balancing.

3. Leverages the fact that typical WLAN mobility is pseudo-static. So clients will not move significantly from the places where they connect. Even in case of mobility, the disruption is minimal.

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Wireless Channel Power Control

Our ideas for a hybrid approach for channel power control have been discussed here:

S. Ganu, G. Bhanage, P. Narasimhan, "System and Method for Computing Coverage Set and Resource Allocations in Wireless Networks", US Patent App. 13/563,500, 2014.

The key difference as noted in the application is that in some cases we propose using a combination of centralized and de-centralized channel power control i.e. the main channel allocation is done centrally and the local channel flips (based on radar etc) are done locally by the access point.

We propose doing a 2 phase channel allocation strategy:
1. Anchor channels: The baseline RF characteristics of a deployment rarely change i.e. the relative position of the infrastructure APs does not change, the other architecture of the building and basic coarse grained pathloss do not change over large time frames. We use this knowledge to come up with a coarse grained anchor channel assignment for each access point. This anchor channel will be a home channel based on the available

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WLAN Interference control through Antenna Selection (ASEL)

In this work, we present a novel, robust scheme for high density WLAN deployments. This scheme uses well known selection diversity at the transmitter. We show that our scheme increases the number of simultaneous transmissions at any given time without excessive overhead (compared to other schemes such as Multi-user MIMO). Furthermore, this scheme can be easily implemented using existing standards.

The main contributions that come out of this report are:

1. a simple method to tackle interference in the network by selecting the best antenna during 

transmission. 

2. A high potential to reduce the collisions for hidden node terminals. 

3. Further, we also proposed a mechanism to account for the next wave of 802.11ac by allowing simultaneous transmission from multiple APs on the same channel.

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WiFi: PP-AMSDU versus SPP-AMSDU a brief comparison

Before we jump into the different type of AMSDUs supported, let us do a quick recap of where AMSDUs fit in with the aggregation hierarchy. Here is an image from Wikipedia:

MSDU, MPDU and PPDU

Multiple MSDUs aggregate to form an AMSDU. Multiple of these will form an AMPDU. The different type of AMSDUs are defined in the WGs documents:

3.114n Payload Protected A-MSDU (PP A-MSDU): An A-MSDU that is CCMP protected but does not include the A-MSDU Present field (bit 7 of the QoS control field) in the construction of the AAD. 

3.135n Signaling and Payload Protected A-MSDU (SPP A-MSDU): An A-MSDU that is CCMP protected and does include the A-MSDU Present field (bit 7 of the Qos control field) in the construction of the AAD.

Uplink Airtime Fairness Control

Problem statement:
There is currently no direct way to control uplink airtime usage of wireless clients on a WLAN without actually implementing something on the client. This is not always possible because of multiple reasons:
Diversity in the operating systems and hardware of client devices.
Privacy issues
General aversion to install 3rd party control software.

Abstract of the idea:
In this case, we address the issue of limiting the airtime used the clients in the uplink direction by controlling the TCP window size in the uplink direction. We do this by doing a deep packet inspection of open TCP sessions for every client and then appropriately limiting the advertised TCP window based on bandwidth consumption by the clients.
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Multiuser support in WLANs versus Cellular networks

About a year back I was reading about the physical layer design of 802.11ac networks, and I started wondering about what would be the similarities or differences between cutting edge cellular networks and WiFi networks. The reason I started thinking about this is because cellular networks seem to be gradually moving towards smaller cells (nano-cell, pico-cell designs), which are similar in RF footprint to regular WLANs.