The InterOp Insider

The UNH-IOL’s Women in Technology (WIT) group was pleased to hold their first event here at the UNH-IOL on Wednesday, August 27th. WIT is a recently formed group at the lab that I have the pleasure of serving as a co-chair along with Marion Dillon, Home Networking Manager, Home Networking Technologies. The event, titled “Women in Industry”, featured four women panelist, all of whom work in tech related industry jobs. Before I get too far, here is a little background about the WIT group at the lab. WIT was formed to represent and provide support for women who work in the tech field (including the ladies at our own lab). We hope to to attract females to STEM degrees as well as the lab. We want the lab to be an open place where everyone feels welcome and supported.

Packet aggregation is the idea of creating packet fragmentation which reduces time on a busy WM and makes error recovery much easier. 802.11e was the first standard to outline a different form of packet aggregation known as A-MPDU (Aggregated MAC Protocol Data Unit). MPDU is what we know as an 802.11 packet, making A-MPDU per packet aggregation.

Each transmission burst in 802.11 requires a guard interval that makes it so transmissions do not interfere with one another. Normally this is an 800ns timer that allows for time between bursts. This gives a safe time between transmissions. 802.11n outlined the idea of a short guard interval, decreasing the timer to 400ns. This gives less time between transmissions, which could potentially cause collisions between transmissions from the same device. In tests done in a closed environment, there was a definite increase in packet error rate. Without SGI, there was little to no packet error. With SGI, we saw a 30% increase in packet error rate. This is a significant increase in error, meaning that far more collisions are occurring. However, the throughput of a BSS using SGI was significantly better than a BSS that does not. While the error increased as predicted, the error did not affect the much higher rates that SGI predicted. Is this true in an uncontrolled environment?

Modulation schemes have not changed much in 802.11, since the early days we used OFDM (Orthogonal Frequency Division Multiplexing). 802.11b was really the only notable 802.11 PHY (physical layer) standard that did not use OFDM but then again it did only get 11Mbps using DSSS (Direct-Sequence Spread Spectra). OFDM is the primary modulation suite used for today’s technology. This is because of the super extensible QAM (Quadrature Amplitude Modulation) with BPSK (Binary Phase Shift Keying), and QPSK (Quadrature Phase Shift Keying) handling the simpler modulation.