Wireless System basic Overview

This page describes wireless system overview with block diagram including baseband,RF and ADC/DAC. It covers speeds/data rates of major wireless networks deployed across the world. It provides links to wireless systems used in North America,Europe and Japan.

A wireless system is the system providing the service to the user using electro-magnetic waves. These EM waves are transmitted and received by the antenna of different types based on the application. Early days of wireless systems were developed for voice communication. Later, text based data transmission systems were developed which were designed for lower speed of transmission. With the invent of higher order of modulations such as 64QAM and 256QAM coupled with MIMO much higher data rates are achieved. To have correction at the receiver in the case of noisy channel environments forward error corrections(FECs) have been devised. various FEC techniques such as convolution coding and convolution turbo coding have been developed for the same.

There are two main parameters viz. coverage distance and data rate which is very important in the design of wireless system. The simple way to achieve higher distance or coverage is by transmitting higher power. Repeaters are also used in a long distance communication before the signal is completely degraded to be recovered. Advanced techniques such as beamforming is in use to have more directional focused antenna beam patterns.

The higher data rate is achieved using higher modulation schemes such as 16QAM,64QAM,256QAM and so on. 16QAM carry 4 bits per carrier,64QAM carry 6 bits per carrier and 256QAM carry 8 bits per carrier.

Further recently multicarrier systems based on OFDM modulation technique have been developed which includes WLAN,WiMAX,LTE etc. Due to simultaneous transmission of data over multiple carriers, higher data rate can be achieved using these OFDM/OFDMA techniques. As shown in the block diagram below, Wireless system consists of three main basic subsystem viz. Baseband, RF and A-D/D-A converters as mentioned in the figure below. Modulation scheme,FEC and OFDM are part of baseband module.

RF part makes sure to have transmitters and receivers in the frequency band of interest to meet frequency regulations as per country wide requirements.

Block Diagram

Baseband Part:
Base band part mainly helps retrieve information correctly at the other end and also make it feasible to transmit through the channel. It consists of Source Encoder, Forward error correction module (CC or CTC) and Base band Modulator (BPSK, QPSK, 16QAM, 64QAM)

A to D and D to A converters:
It converts Digital data into Analog form at the Transmitter. The output is modulated IQ data at IF Frequency. This will be the input to RF Up converter. At receiver ADC is used which converts modulated IQ data at IF into digital data.

RF Part:
It consists up converter/power amplifier at the transmitting end and LNA / down converter at the receiving end. Antenna is used to convert signal into electro-magnetic form and vice versa to Transmit/Receive the signal in to the air. OMT makes it possible to use the same antenna for both transmit and receive OMT is basically a transmit reject filter which blocks signal to be transmitted while Antenna is receiving the signal from the other end.

Types of networks

Wireless networks are divided based on user perspective parameters. The main characteristics which forms types of networks are as follows.Various wireless standards and proprietary standards exist to define the specifications to be followed by manufacturers of wireless equipments to provide the service to the community.
•  Fixed OR Mobile
•  Point to Point(PTP) OR Point to MultiPoint(PMP)
•  Licensed OR Unlicensed

Fixed: This type of network is the one which will have both source and destination fixed at one location. The one example is point to point(PTP) terrestrial microwave radio link. The other networks are WLAN and WiMAX based on 802.11 and 802.16 IEEE standards. Point to Point and Point to Multipoint networks in both licensed and unlicensed categories are available in frequency range from 1GHz to about 90GHz.

Nomadic: These networks are the one providing individuals with high speed data access in many of the public and private places. They are not actually mobile networks but some sort of mobility is permitted as if person is walking or moving form one place to the other place. One such network is 802.11b based WiFi network.

mobile: In this network higher speed of mobility is involved between user and the bas station of wireless system providing the service. Usually base station is fixed and mobile subscribers/PDAs/tablets/Laptops will be moving through some means of transport. The example of such systems are Mobile WiMAX(16e),WCDMA,GSM,LTE,LTE-Advanced etc.

Types of Topologies

P2P Topology: In this topology, voice or data service is point to point. For example, between Access Point and Station directly in the case of WLAN or WiFi network.

PMP Topology: In this topology service is point to multipoint. For example, between base station to multiple subscribers or users in GSM,CDMA,LTE and WiMAX networks.

Wireless network speeds

Following table mentions wireless network speeds/data rates including major mobile broadband standards viz. WiMAX,GSM,CDMA,UMTS,LTE,LTE-a or LTE-Advanced etc. As described earlier speed depends on various parameters such as higher modulation schemes 64QAM/256QAM,multiple antenna techniques such as MIMO and symbol duration/period.

wireless systems across the world

Following are links to mobile radio standards or wireless network systems used in North America,Europe and japan.

Mobile Radio Systems in North America
Mobile Radio Systems in Japan
Mobile Radio Systems in Europe

Throughput calculations

Following are links for useful throughput calculations for LTE,GSM,GPRS and EGPRS systems.

LTE throughput
GSM,GPRS,EGPRS throughput

RF and Wireless Terminologies