Comprehensive Analysis of Application of OFDM technology in various fields

From the technical perspective, the fourth generation of mobile communication systems is expected to take OFDMOrthogonal Frequency Division Multiplexing as the core technology, the main reason is the high efficiency of radio frequency, strong anti-noise ability, and high-speed data transmission. However, there are still many problems to be solved in OFDM, but some standards have come to an end and will be commercially used, such as digital audio broadcast.) Currently, OFDM technology has been widely used in Wireless LAN, however, it will take time to apply it in the mobile communication field.

At present, OFDM technology has been widely used in broadcast audio, video and civil communication systems. Its main applications include Asymmetric Digital user loop ADSL and ETSI standard digital audio broadcast DAB) digital Video Broadcast (DVB), High Definition TV (HDTV), wireless MAN, wireless LAN WLAN), and even 3G CDMA have begun to introduce the OFDM technology to improve its performance.

No stranger to technology

OFDM orthogonal frequency division multiplexing (OFDM) is a high-speed transmission technology in wireless environments. As we all know, the frequency response curves of wireless channels are mostly non-flat, and the main idea of OFDM technology is to divide a given channel into many orthogonal subchannels in the frequency domain, one sub-carrier is used for modulation on each sub-channel, and each sub-carrier is transmitted in parallel. In this way, although the total channel is non-flat and frequency-selective, each sub-channel is relatively flat and performs narrowband transmission on each sub-channel, the signal bandwidth is smaller than the corresponding bandwidth of the channel, so the interference between the signal waveforms can be greatly eliminated. Because the carriers of subchannels in the OFDM system are orthogonal to each other, their spectrum overlaps with each other, which not only reduces the mutual interference between subcarriers, it also improves the spectrum utilization ,. On the other hand, the OFDM technology also has defects: It is very sensitive to frequency offset and phase noise. The peak-to-average power ratio is relatively large, and the increase of this ratio will reduce the efficiency of the RF amplifier.

Increasingly widely used

In recent years, there have been a lot of research efforts and progress has been made on the two defects of OFDM. The OFDM technology can be used in both mobile wireless networks and fixed wireless networks. It switches signals between floors, users, transportation tools, and the scene, this effectively resolves information conflicts.

Field 1: Digital TV broadcasting with High Definition

OFDM has been widely used in digital broadcast and television systems. Among them, the digital audio broadcast DAB standard is the first standard to officially use OFDM. In addition, all the modulation technologies used in the international digital high definition television transmission system include the OFDM technology, and the European HDTV Transmission System has adopted the COFDMcoded OFDM: encoding OFDM technology. It has a high spectrum utilization rate, which can further improve the anti-interference capability and meet the transmission requirements of the TV system. The main reason for selecting OFDM as digital audio broadcast and digital video broadcast DVB is that the OFDM technology can effectively solve the problem of multi-path latency extension.

Therefore, it is not difficult to see that the good performance of OFDM technology has made it widely used in many fields. The European DAB system uses the OFDM modulation technology. Its experimental system is already running and soon attracted a large audience. It significantly improves the performance of mobile wireless broadcasting, and the development of the complete set of DAB chips is under development in a European development project, which will greatly reduce the price of OFDM Receivers, its market prospects are very promising.

Field 2: Wireless LAN

As you know, the HiperLAN/2 physical layer uses the OFDM and Link adaptive technology, and the media access control MAC layer uses the connection-oriented, centralized resource control TDMA/TDD mode and wireless ATM technology, the maximum speed is 54 Mbps, and the minimum practical application can be kept at around 20 Mbps. In addition, the IEEE 802.11 Wireless LAN works in the ISM license-free band. The IEEE 802.11a and IEEE 802.11g standards adopting OFDM technology are defined in the 5.8GHz and 2.4GHz frequencies respectively, the maximum data transmission rate is increased to 54 Mbps.

The continuous development of technology has led to integration. Some key 4G and 5G technologies, such as OFDM, MIMO, smart antennas, and software radio, are applied to wireless LAN to improve WLAN performance. For example, 802.11a and 802.11g adopt OFDM modulation technology to increase the transmission rate and network throughput. The 802.11n plan combines MIMO with OFDM to multiply the transmission rate. In addition, the antenna technology and transmission technology greatly increase the transmission distance of the wireless LAN, which can reach several kilometers and ensure the transmission rate of Mbps ).

For multimedia services to be carried out in the wireless LAN in the future, the data transmission rate of up to 54Mbps is far from enough. To further improve the data transmission rate of the wireless LAN and achieve seamless integration of wired and wireless LAN, IEEE established an IEEE 802.11n team to develop a new high-speed wireless LAN standard. IEEE 802.11n plans to increase the transmission rate of WLAN from 54Mbps of 802.11a and 802.11g to above Mbps, and the maximum speed can reach 320 Mbps, making it another major event after 802.11b/a/g. Different from the 802.11 standard, the 802.11n protocol uses dual-band operating modes, including GHz and GHz ). In this way, 802.11n ensures compatibility with the previous 802.11a/B/g standards.

Field 3: Broadband Wireless Access

The OFDM technology is suitable for high-speed transmission in wireless environments. It is not only used in Wireless LAN, but also used in Broadband Wireless Access to BWA. The IEEE 802.16 Working Group is dedicated to BWA technical work. It has developed a 2 GHz ~ 11 GHz BWA standard-IEEE 802.16a, the physical layer uses the OFDM technology. This standard is not only a new generation of wireless access technology, but also plays an important role in the future development of cellular mobile communication.

In the BWA field, some companies develop technologies based on OFDM, but they have their own characteristics to form some patented technologies, such as Vector ofdmvoofdm of Cisco and Iospan), Wideband OFDMWOFDM of Wi-LAN Company), flash-OFDM of Flarion company. Among them, voofdm is supported by Cisco, and WOFDM is proposed by Wi-LAN, which forms two camps of OFDM Based on two organizations: broadband wireless Internet forum BWIF) and OFDM forum, they try to make their own OFDM models a standard. Among them, the OFDM Forum, sponsored by Wi-LAN, has more than 50 members, including Breezecom, start-up BeamReach Networks, and Nokia, it is mainly to coordinate the submission of the ieee ofdm proposal. The broadband Internet forum BWIF is under the initiative of Cisco, established by IEEE industrial standards technology organization IEEE-ISTO, its main goal is to provide low-cost broadband wireless access technology, we call for the adoption of voofdm-based standards as a solution.

Field 4: New Concept of 3G CDMA

In order to meet the needs of wireless multimedia communication in the future, people are stepping up the commercialization of the 3G system, while starting the study of the last 3 GBeyond 3G. In terms of technology, 3G mainly uses CDMA technology as the core technology, while in the future, mobile communication systems will be most noticed by OFDM technology. In the broadband access system, due to the excellent characteristics of the OFDM system, it will become a powerful support for the next generation mobile communication network.

Another fact is that 3G networks are currently facing many problems. For example, its data transmission speed is far below the advertised 2 Mbps, and its actual transmission speed is only about Mbps, when the network is busy, the speed may not reach 1/3. This situation is only enough to transmit high-quality audio. Users may need to wait for high-quality videos.

To combat multi-path interference, CDMA technology requires more complex balancing and modulation, which is very difficult to implement. In order to promote the development of 3G, people began to study the advantages of OFDM technology into CDMA system, launched MC-CDMA technology. Compared with ordinary DS-CDMA, MC-CDMA system has the following advantages:

1) more flexibility. For example, the flexibility brought about by adding protection time to OFDM signals can achieve optimal spectrum utilization in different cell environments;

2) high capacity and high performance. Because of the frequency intertwined, the system provides more than one number of frequency diversity, so we can use different detection methods to fully explore the gains provided by such diversity;

3) high anti-interference Performance;

4) No balance is required. Due to the characteristics of multi-carrier modulation, it divides high-speed signals into multiple low-rate signals, so that the interference between the signal waveforms is eliminated, so there is no need for balance.

To sum up, at the turn of the times, the integration and upgrade of old systems are the topics of industry concern. Currently, we are talking about how to upgrade GSM to the third generation mobile communication system, in the future, how will CDMA be combined with OFDM technology? It can be predicted that CDMA will never disappear in the fourth generation mobile communication system, but will become a part of its Application Technology. Maybe there will be new integration technologies such as OFDM/CDMA in the future. In fact, the technology actually used in the digital audio broadcast mentioned above is the Integration Technology of OFDM/FDMA, and the combination of the two technologies. Therefore, in the future, the fourth-generation mobile communication system with OFDM as the core technology will also combine the advantages of the two technologies.