Single Carrier FDMA - for 4G wireleess

Over the last decade, the bit rates achieved in wireless communications systems have increased steadily.
TDMA and CDMA has been the major technologies in multiple access. The highest bit rates in commercially deployed wireless systems are achieved by means of Orthogonal Frequency Division Multiplexing (OFDM). The next advance in cellular systems, under investigation by the Third Generation Partnership Project (3GPP), also anticipates the adoption of OFDMA to achieve higher bit rates. Single carrier frequency division multiple access (SC-FDMA), a modified form of Orthogonal FDMA (OFDMA), is a promising technique for high data rate up-link communications in future cellular systems.

SC FDMA
An SC system transmits a single carrier, modulated, for example, with QAM, at a high symbol rate. The transmitters use different orthogonal subcarriers to transmit information symbols. The transmission is sequential, which reduces the variations in the transmitted signal envelope. This results in a lower peak-to-average-power ratio. Frequency domain equalization os carried out to counter the severe delay spreads the signal might encounter. The advantages may be listed as:

• Small variations in the instantaneous power of the transmitted signal
• Possibility for low-complexity high-quality equalization in the frequency domain.
• Possibility for FDMA with flexible bandwidth assignment.
• SC-FDMA can be seen as normal OFDM with a DFT-based precoding

SC-FDMA transmitter and receiver
The block diagram of the SC-FDMA receiver and transmitter is given the figure. The figure is self-explanatory. Similar to OFDM modulation, DFTS-OFDM relies on block-based signal generation.
By adjusting the transmitter DFT size and the size of the block of modulation symbols the nominal bandwidth of the DFTS-OFDM signal can be dynamically adjusted.

Throughput
Information throughput is another indication of the system performance. Here the throughput depends on the manner in which information is applied to the subcarriers. The two main methods are localized and distributed. The benefit of distributed system, compared to localized, is the possibility for additional frequency diversity as even a low-rate distributed signal can be spread over a potentially very large overall transmission bandwidth. It has been shown that the SC-FDMA can be tuned to achieve data rates in excess of 40Mbps.

Future
Within a specific SC-FDMA system configuration, there are many design and operational choices that affect performance in a complex manner . The impact of channel estimation error on the throughput performance of SC-FDMA is still not understood clearly. Still, SC-FDMA is a promising technique for high data rate
uplink communication in future cellular systems.

Wireless Communication Equipment..

A big market exists for wireless applications today. Companies are offering a wide range of radio modules for wireless applications, and it is difficult to choose between them. For a change, we look into some of the radio interface modules which are available in the market. The key factors that are considered are the power consumption, integration ease and range, features and finally the usability or functionality. Some are suitable for industrial applications also. A variety of antenna options are also available for the products. A list of companies which have products which are worth a look are listed in the following sections. Typical products of some companies are given below for a fast look up.

Aerocomm is one company to watch out for if you are looking for the fastest way to go wireless, since they seem to have a wide range of products. The company claims to offer compact transceivers, which are ready to integrate, and offers technology that ensures reliable communication even in frequency-polluted areas. The industrial and commercial range includes 2.4GHz/900MHz RF transceiver modules and the Zigbee transceiver module. The ZigBee transceiver (ZB2430) is an SoC compliant module. This is available in two versions to suit varying requirements. The ZB2430 and ZB2430-100 are two where the latter is offers an extended communication capability. The ZB2430 uses 2.4GHz ISM band, so OEMs looking for standardization can use it. The module comes as either full-function devices or reduced function devises.

Data Hunter offers an OEM WLAN serial server module, typically targeted at portable, low cost equipments. It supports the major network/protocol standards like TCP/IP, UDP/IP, HTTP, ARP, SNMP etc. It also uses the 2.4GHz band typically upto 2.48GHz. It has a very useful power-save mode, which is helpful in low-power applications. It is named 802.11b "Mini-b" module as given in their website.

Air-wave offers AWM630, a new range of wireless modules operating on again, the 2.4GHz ISM band. The company claims that the devices are FCC compliant, so a global market is the target. Typical applications for the AWM630 may be for professional or domestic sound/video transmissions, security systems, or public information systems. The video compatibility for both PAL and NTSC is present in the same module. A stereo audio is also supported. The AWM630 series is RoHS compliant, that is what the company claims. The prices are very competitive and the modules are available through saelig.

Conexant is another company which offers a single chip 802.11b WLAN compatible device for small, embedded portable applications. The company offers CX53113, a low power , small form factor module which is suitable for mobile applications. It also operates in the 2.4GHz ISM band, supporting data rates up and above 6Mbps.All the above products are targeted at different end-markets but have a lot of things in common. It is just a pointer as to where to look for if you are intending to cut cables from your application and intend to do it fast!!!