Wireless System Overview: Baseband, RF, and Data Rates

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

A wireless system provides a service to the user using electromagnetic waves. These EM waves are transmitted and received by antennas of different types based on the application. Early wireless systems were developed for voice communication. Later, text-based data transmission systems were designed for lower transmission speeds.

With the invention of higher-order modulations such as 64QAM and 256QAM coupled with MIMO, much higher data rates are achieved. To ensure correction at the receiver in 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 this purpose.

Two main parameters—coverage distance and data rate—are critical in designing a wireless system. The simplest way to achieve a greater distance or coverage is by transmitting higher power. Repeaters are also used in long-distance communication before the signal is completely degraded and needs to be recovered.

Advanced techniques like beamforming are used to create more directional, focused antenna beam patterns. Higher data rates are achieved using higher modulation schemes such as 16QAM, 64QAM, and 256QAM. 16QAM carries 4 bits per carrier, 64QAM carries 6 bits per carrier, and 256QAM carries 8 bits per carrier. Furthermore, multicarrier systems based on OFDM modulation techniques have been developed, including WLAN, WiMAX, LTE, etc. Due to the simultaneous transmission of data over multiple carriers, higher data rates can be achieved using these OFDM/OFDMA techniques.

As shown in the block diagram below, a wireless system consists of three main basic subsystems: Baseband, RF, and A-D/D-A converters. Modulation schemes, FEC, and OFDM are part of the baseband module. The RF part ensures that transmitters and receivers are in the frequency band of interest to meet frequency regulations as per country-wide requirements.

Block Diagram

The wireless system block diagram is composed of:

1. Baseband
2. RF
3. A-D/D-A converters

Baseband Part

The baseband part mainly helps retrieve information correctly at the other end and makes it feasible to transmit through the channel. It consists of a Source Encoder, a Forward Error Correction module (CC or CTC), and a Baseband 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 of an up converter/power amplifier at the transmitting end and an LNA / down converter at the receiving end. An antenna converts the signal into electromagnetic form and vice versa to Transmit/Receive the signal into 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 the signal to be transmitted while the Antenna is receiving the signal from the other end.

Types of Networks

Wireless networks are divided based on user perspective parameters. The main characteristics that form types of networks are as follows. Various wireless standards and proprietary standards exist to define the specifications to be followed by manufacturers of wireless equipment to provide service to the community.

• Fixed OR Mobile
• Point to Point (PTP) OR Point to MultiPoint (PMP)
• Licensed OR Unlicensed

Fixed: This type of network has both source and destination fixed at one location. One example is a 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 the frequency range from 1GHz to about 90GHz.

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

Mobile: In this network, a higher speed of mobility is involved between the user and the base station of the wireless system providing the service. Usually, the base station is fixed, and mobile subscribers/PDAs/tablets/laptops will be moving through some means of transport. Examples 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 a WLAN or WiFi network.

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

Wireless Network Speeds

The following table mentions wireless network speeds/data rates, including major mobile broadband standards like 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.