Linux: Compare if two files are the same

Quick script I wrote in my .bashrc to check if two files are the same:

#md5sum

function md5comp()

{

    a=$(md5sum $1 | awk '{print $1}')

    b=$(md5sum $2 | awk '{print $1}')

    echo "Comparing $1 and $2"

    [ "$a" = "$b" ] && echo  "Equal" || echo "Not Equal"

}

WiFi: PER based adaptive AMSDU aggregation worth the effort?

This has been a lingering question. A lot of studies (including one of ours) in the past has delved into the support for AMSDU aggregation - and the ability to consider PER as a factor for adaptively controlling AMSDU aggregation. But is it worth the computational effort? Can this be simplified by making AMSDU aggregation static and using other mechanisms for limiting PER?

Difference between Active and passive beamforming mechanisms

Active beamforming is the mechanism used in WiFi access points and clients where the beamforming is done with different chains on a transmitting radio (usually using active components like transistors). Passive beamforming on the other hand is achieved by using passive components (resistors, capacitors, and inductors) to introduce phase and amplitude variations across different path such that we are able to achieve constructive addition in some cases which results in beamforming.

The main differences between these two mechanisms: 

• Butler matrices are a passive beamforming and channel model rendering mechanism.
• Beamforming can be useful against jamming attacks to increase SNR at client.
• Passive beamforming networks are better because active components are more susceptible to change in temperature and other environmental factors.
• Compared to active beamforming networks, passive beamformers can be made electrically stable and reliable across a wide range of operating conditions, although a great deal of flexibility in the physical layout may be needed to accommodate a large variety of connector interfaces for different antenna arrays.

References

* Miscellaneous articles on butler matrices

* Understanding Passive Beamforming Networks http://defenseelectronicsmag.com/military-defense-electronics/understanding-passive-beamforming-networks

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.

WiFi: Comparison of WiFi Direct vs WiFi Aware vs BLE vs Adhoc mode (802.11)

Summary
WiFi Aware - service discovery that helps setup WiFi Direct links.
BLE - service discovery and P2P connection.
WiFi Direct - P2P connection
WiFi Adhoc mode - basic P2P connection (legacy mechanism)

We will now differentiate between each of these protocol suites and their applications.

WiFi Aware vs BLE
- WiFi Aware has a longer range (because of wifi power limits)
- works with existing WiFi chips (protocol overlay - Phy is mostly the same)
- higher bandwidth than BLE (faster for gaming etc) - this is because it will use WiFi Direct once wifi aware discovers the service.

- WiFi aware works across brands of phone vs ibeacons which will work only on iPhones for e.g.

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.