LTE, WiMAX big PK 4G wireless standard is better?

Both Long Term Evolution (LTE) and WiMAX technologies use advanced methods, such as Orthogonal Frequency Division Multiple Access (OFDMA) and Multiple Input Multiple Output (MIMO), and they are all based on IP (Internet Protocol) With high-speed data function, it can implement advanced applications such as fast Internet access and video. The International Telecommunication Union (ITU) defines LTE and WiMAX as 3G. Some experts believe that these two standards are close to 4G, more like 3.9G.

Although these two systems seem to be fiercely competitive, one will eventually win and one will be eliminated, but this may not be the case. There may be competition in data services in some regions, but this does not mean all. These two standards were developed in different historical contexts, and now have their own different uses. LTE is obviously the successor of cellular technologies such as UMTS / WCDMA / HSPA and CDMA2000 3G, while WiMAX is mainly used for broadband wireless connections and backhaul links.

LTE technology

LTE technology is developed from the earliest GSM voice technology, GPRS and EDGE for data transmission to the current UMTS WCDMA and HSPA advanced 3G technology. Most of this standard has now been completed, but it has not yet been finalized. LTE is currently undergoing a lengthy ITU standardization process and is expected to be completed later this year.

Most cellular operators agree to use LTE as a 4G standard, allowing almost everyone in the world to enjoy the happiness brought by the new technology. These operators include Verizon and Sprint in the United States, and they use a CDMA2000 standard that is different from the UMTS WCDMA standard. China hopes to adopt LTE variants based on time division multiplexing (TDD) instead of frequency division multiplexing (FDD). So far, more than 30 operators have agreed to adopt LTE, and plan to integrate LTE into the system in the near future.

At present, the LTE systems in operation are all experimental systems in various regions of the world. Some formal LTE will be visible by 2010, but most operators have hinted that large-scale deployment will begin in 2011 or after 2012.

The industry is still actively promoting 3G systems that are still very new, and these systems are working very well. However, LTE is an inevitable choice. Larger user capacity and higher data rates not only support current and future video services, but also support data-intensive services, such as mobile Internet access.

LTE is a wireless standard specifically designed for mobile applications, with downlink data rates up to 100Mbps and uplink rates up to 50Mbps. In contrast, the maximum downstream rate of most HSPA 3G services is only 14Mbps, and the upstream rate is only 5.7Mbps. The updated HSPA standard defines the maximum downlink and uplink rates as 84 Mbps and 22 Mbps, respectively, but this system has not yet been commercialized. These high rates of LTE allow users to smoothly access video, Internet services, games and other data-intensive applications.

Current WCDMA and HSPA channels use 5MHz bandwidth, while LTE designs use different bandwidths, including 1.4, 3, 5, 10, 15 and 20MHz. Each bandwidth uses 128, 256, 512, 1024, 1,536, and 2,048 fast Fourier transform (FFT) sub-channels.

In principle, LTE can work normally on any cellular frequency that is currently allocated and has sufficient bandwidth, but not all frequencies are suitable for a wider bandwidth mode. In the US, LTE will operate in the 2.1 GHz band and 700 MHz allocated frequency.

LTE is a strict FDD technology, and its transmission and reception frequency bands are separated from each other. The frequency isolation of the downlink and uplink is not fixed, and the variation range on the lowest frequency band is from about 12MHz to 18MHz, and up to 340MHz to 560MHz on the higher frequency. Higher data rates require wider bandwidth and use a lot of spectrum space.

Quadrature phase shift keying (QPSK), 16-phase quadrature amplitude modulation (16QAM), and 64QAM are commonly used modulation techniques for LTE, depending on the available bandwidth and data rate requirements. LTE supports different modes of MIMO, including 4x4, 2x2, 2x1, and 1x1 for the downlink. Typical cellular capacity is around 200 at 5MHz bandwidth. The wider bandwidth can increase the number of users per cellular base station to more than 400. The spectral efficiency is in the 5bit / Hz range, but it depends on the physical layer (PHY) details.

OFDMA is only used in the downlink, and the uplink radio technology is single carrier frequency division multiple access (SC-FDMA). The main reason for choosing OFDMA is to reduce the power consumption of mobile phones. The peak-to-average power ratio (PAPR) of this technology is smaller than OFDM, but it means that simpler RF power amplifiers can be used. This technology supports 1x2 and 1x1 MIMO modes.

LTE is a cellular telephone technology, but it can also be applied to high-speed broadband wireless connections, such as USB adapters and data cards, or embedded into notebooks and netbooks. In these areas, LTE will compete directly with WiMAX. LTE femtocells also enable high-speed services to enter the home directly.

Although there is no LTE infrastructure yet, ITU and 3GPP are already studying the true 4G technology. This 4G technology is called IMT-Advanced, and it defines a more advanced LTE version. In particular, the mobile data rate of IMT-Advanced or LTE-Advanced will exceed 100Mbps, and the fixed or roaming rate may reach 1Gbps. Obviously, reaching these targets depends on higher bandwidth (> 20MHz), larger MIMO mode and other technologies. Nevertheless, it will take years for people to see this standard or its application.

LTE deployment issues

In addition to the high cost of cellular systems due to the use of new technologies, operators also face other key issues, including the difference between switched and packet systems, the need for more base stations, voice service roles, and insufficient backhaul links. All current cellular systems are circuit-switched systems, and LTE is a packet-based system.

This means that operators need to continue to retain the original circuit-switched systems and equipment in order to provide traditional services to old users and some current users. But at the same time, the new packet system must be implemented and compatible with all existing systems.

In the US, LTE will initially use higher cellular frequencies around 2.1 GHz and 2.6 GHz. At this frequency, the coverage of the cellular base station is much smaller than the typical 800MHz or 900MHz base station, so more base stations are needed, which greatly increases the cost. The only hope is to use the latest 700MHz allocated frequency bands owned by some operators. The coverage of base stations at this frequency is comparable to current base stations, or even slightly better.

LTE is a packet data system. There is no need to consider voice services when designing, so operators will undoubtedly face the problem of how to implement voice on LTE. There are three systems to consider.

The first is circuit switched (CS) fallback, allowing operators to use existing circuit switched 3G technology to handle LTE voice. The second is the IP Multimedia Subsystem (IMS). In this case, the network can handle any service. The third system is to transmit voice over LTE universal access (VoLGA), in which case circuit-switched voice is transmitted over the LTE network through a tunnel.

Finally, most cellular networks have insufficient backhaul channels, especially for applications with heavy 3G services. Therefore, full deployment of LTE is indeed a good solution. This means eliminating millions of T1 and T3 lines, adding faster microwave backhaul, and even using fiber optic backhaul where feasible.

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