Key Technologies And Wireless City Development Strategy Analysis
, Mind as an extension cable to achieve a fixed wireless Internet access
, with wireless access technology, continuous development and people's understanding of city informatization the deepening of the city has grown to wireless to broadband mobile Internet-based communication medium , combined with the user's basic properties (identity, habits, preferences, etc.), as at any time for the municipal services, health care, tourism, personal life, and so the proliferation of a variety of services.
In the real world, the concept of wireless city in full swing, but the actual deployment was unsatisfactory, in 2007, the U.S. major cities of the wireless city plan in just 2 years after becoming popular in the tasteless, the U.S. announced the cancellation of a number of cities or suspension of the project. In the end is what causes the advanced technology, high interest, a bright future of wireless application experience cold city? This paper attempts to drive the critical needs of technology, combined with the development of key technologies, an explanation, and in this technology for the future development of wireless city, give their views.
2 Analysis of key technology of wireless cities
With the birth of WiFi wireless LANs, especially 802.11b series of communications chips embedded Intel's CPU, making wireless Internet access possible, but also gave birth to "wireless city" needs. People are not satisfied with a fixed place of office online, share information, government departments also hope to organize information resources more effectively and better serve the public. So, led by IT sector wireless access technology from the wireless local area network gradually expanded to all levels, up to wireless local area network, wireless metropolitan area network, wireless WAN, wireless personal area network down there, while the industry to actively absorb CT advanced technology and experience to enhance the network capacity could be operating to schedule, comprehensive, multi-level coverage of all communications needs.
Can be said that wireless technology is derived from the city in the IT sector, with WiFi, WiMAX and other technologies to represent and draw the CT industry to IMT-2000, IMT-Advanced as the representative of the mature experience and technology, based on the fusion of IT and CT, have the following key technologies for the selection of points discussed. Key technologies
Order to facilitate the elaboration of the following in accordance with the physical layer on the bottom-up, MAC layer and network layer selected discusses some key technologies.
1) physical layer OFDM: Orthogonal Frequency Division Multiplexing is a modulation technique, the core is through the wide signal bandwidth into several orthogonal self Road, and make confident Road, less than the bandwidth of the relevant channel bandwidth, and through the introduction of timing offset (frequency domain CP) makes the signal change in the protection of intervals without causing ICI (ICI) and inter-symbol interference (ISI) to be effective against multi-path effects, making large-capacity non line of sight transmission signal possible.
OFDMA: multiple access based on OFDM modulation mode can be used for downlink. OFDM modulation signal through a flexible subcarrier allocation (such as: the adjacent subcarrier allocation and distributed subcarrier allocation) to meet the needs of different scenarios, such as fixed or nomadic applications in the scenarios, using the township subcarrier allocation ways to make individual subchannels with higher signal to noise ratio; the distributed subcarrier allocation algorithm can make sub-carrier spread throughout the band, although do not appear very good or very bad channel environment, but with a certain mobile application and comparison of application scenarios. According to sub-carrier signal to noise ratio, in different sub-carrier modulation using a different encoding, you can maximize the channel utilization.
GMC: the generalized multi-carrier, is for the uplink multiple access scheme, combined with OFDMA applications. The inverse transform filter (IFBT) to achieve frequency division multiplexing and frequency division multiple access approach, with OFDMA the way has a low PAPR and can more effectively resist the uplink user timing and frequency synchronization between the error caused multi-access interference. The key technical points are as follows:
L complex filter transform theory and fast algorithms
L DFT-based spread spectrum multiple access program GMC
L signal PAR Suppression L Timing Method: protection of sub-band frequency domain and time domain cyclic prefix
L channel estimation and equalization
by: gaga
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