# Channel Model

This page describes channel models viz. awgn,rayleigh,rician and other channel models for wimax,wlan,lte systems.

Channel refers to the path between Transmitter and Receiver whether it may be wired or wireless. Channel model refers to the mathematical modeling or mathematical equation describing the channel behavior between the Transmitter and Receiver.

There are two main types of channels viz. time invariant channel and time varying channel depending on the motion between Transmitter and Receiver. If transmitter and receiver is not moving and is fixed at one location the channel is referred as time invariant channel. The example of time invariant channel is simple cable between transmitter and receiver or fixed wimax system where both Base station and subscriber premises equipment is fixed at one location and are not moving. If transmitter and receiver or any one is moving then the channel is referred as time variant channel. The example of time varying channel is mobile wimax system or cellular system where Base station is fixed but the mobile or internet compatible devices (tablet, ipad, laptop)are moving either at vehicular speed or pedestrian speed.

There are basic channel models known as AWGN, Rayleigh and Rician which are used by communication design engineer for the purpose validating transmitter and receiver under design. For complex communication systems channel models are need to be designed to validate transmitter and receiver. Various parameters such as number of paths, delays at each path, terrain type, Doppler frequency and/or speed are considered in the design of channel model.

AWGN- the short form of Additive White Gaussian Noise, mainly applies to semi-flex or coaxial cable between transmit and receive path or applicable to space communication. It takes care of thermal noise available in the channel or generated in electronic devices at transmitter and receiver. There are matlab functions such as awgn, rand and randn used to model this type of channel. The function randn is used as to generate random numbers with normal distribution with mean of zero and variance of one. The function rand is used to generate random numbers with uniform distribution. Following AWGN equation is popularly used by designers of communication chain.

R=awgn (T, SNR, 'measured' )

Here T is the transmit vector, R is the received vector with noise as per SNR in dB.

Rayleigh- This channel type is applied to channel having only non LOS paths between transmitter and receiver and no dominant or LOS path. The matlab model for this type of channel is rayleighchan.

Rician- This channel type is applied to channel having both LOS and non LOS paths between transmitter and receiver. The matlab model for this type of channel is ricianchan.

Other than the basic channel models mentioned above there are various channel models designed specific to the system as mentioned below.

1. SUI channel model- Designed for fixed wimax system implementation as per IEEE 802.16-2004 OFDM specifications.

2. ITU-T channel model as per ETSI UMTS specifications- Designed for mobile wimax system implementation as per IEEE 802.16e-2005 OFDMA specifications. Include channel coefficients for indoor, pedestrian as well as vehicular channels.

3. JTC channel model- For WLAN channel as per IEEE 802.11 specifications, and one proposed by Naftali Chayat. Used for 11a, 11b and 11g.

4. TGn channel model- For WLAN channel as per IEEE 802.11n specifications.

5. UWB channel model - For IEEE 802.15.3 and IEEE 802.15.4 system specifications.

There are various hardware equipments available from leading test and measurement companies such as Anritsu, Spirent communications, Agilent technologies, azimuth systems and more which emulate channel models for various wireless technologies for test and measurement purpose. These include channel emulators for wireless technologies such as wimax, WLAN, LTE, LTE-advanced, GSM, CDMA, HSPA and more. For more details visit our page on wireless channel emulators in vendors section.