Urban Communication, 802.11a with Knife-Edge Diffraction

The network planning of a local area network in an urban scenario is investigated. The knife edge diffraction method is used.

Sites and Antennas

There are six sites with one sector antenna at each site. Each antenna operates on one of three different carrier frequencies around 2.4 GHz. The frequencies were reduced from 5.2 GHz to 2.4 GHz in the 802.11a standard to increase the communication range. The transmission site antennas are placed at different locations and are directed toward the center to achieve a good data rate over the entire region.

Air Interface

The wireless local area network (WLAN) air interface is defined by an 802.11a wireless standard (.wst) file. OFDM/SOFDMA (orthogonal frequency-division multiplexing) is selected for multiple access. It uses time division duplex (TDD) for switching between uplink and downlink. In TDD, only downlink carriers are defined since uplink and downlink are separated in time. In this model, an adaptive switching method is used depending on the traffic load.
Tip: Click Project > Edit Project Parameter and click the Air Interface tab to view the carriers and transmission modes.

Computational Method

The computational method Empirical Vertical Plane Model: Knife Edge Diffraction is selected. The rays travel in the vertical plane between transmitter and receiver and are diffracted at roof edges.
Tip: Click Project > Edit Project Parameter and click the Computation tab to change the model.


Propagation results show at every location the power received from each transmitting antenna.

The network simulation also calculates the maximum received power and SNIR (max) for all modulation and coding schemes used in this model, for both downlink and uplink.

The figure below shows the maximum data rates. In white pixels, no communication is possible. This can be due to insufficient received power, low SNIR, or both. Remedies could include more antennas, higher mounting, more carriers, or higher transmit power.
Figure 1. Maximum achievable data rate.