Great Achievements in a Small World

——An Analysis of WiMAX Indoor Coverage Solution

By Liu Min

Indoor coverage is the main battlefield for high density and differentiation among operators, especially for WiMAX. On the one hand, because of the spectrum characteristics of WiMAX, where currently in the world, major spectrums of WiMAX include 2.3G , 2.5G and 3.5G, and the fact that the higher the frequency band, the greater the propagation loss and penetration loss of radio wave in the free space, so as compared with 2G/3G network, WiMAX outdoor base stations have greater difficulty in solving indoor coverage. On the other hand, according to the statistics of NTT DoCoMo, although indoor coverage accounts for only 20% of all covered area, over 70% of data service, especially high speed data service, occurs indoor, so indoor coverage is decisive to network quality.

As seen from the experience of mobile operators’ 3G indoor station construction, time synchronization, backhaul transmission and network deployment will be major challenges faced by post-3G system in indoor coverage. How shall operators face up to the challenges and survive indoor coverage competition with technological innovation and feasible solutions, and finally maximize the return on investment? The following is ZTE’s ideas about WiMAX networking based on our experience in radio network construction.

I. Technological innovation tackling the traditional difficulty

WiMAX is a TDD system. For indoor coverage, the first step is to acquire time synchronization. Traditional GPS solution, due to the restriction and high cost of telecom construction, as well as the difficulty in GPS antenna feeder layout, has very limited applications.

Facing the difficulty to acquire time synchronization, ZTE creatively proposed two solutions, namely, using ToP technology or high sensitivity GPS, for indoor Pico BS/Femto.

Based on IEEE1588 protocol, ToP technology can solve indoor GPS antenna installation and indoor coverage problems through packet network transmission and clock synchronization recovery. Besides, ZTE ToP server can also intelligently adjust the parameters of ToP algorithm according to the characteristics of different transmission mediums, so as to better satisfy WiMAX network synchronizations requirements. ZTE is the first vendor supporting IEEE1588 time synchronization solution on commercial base stations. ToP server can support GPS signal provision and distribution upon regional coverage.

 

Figure 1 Working mode of IEEE1588 server

In case of the sporadic deployment of Pico BS/Femto, high precision indoor GPS scheme can be used for time synchronization. The receiving sensitivity of high sensitivity GPS receiver can reach -160 dBm. Therefore, using indoor GPS antenna can ensure that the synchronized signals outputted from GPS can meet WiMAX system requirements, while a normal GPS receiver has a receiving sensitivity of only -143 dBm, requiring outdoor GPS antenna to secure its performance.

In addition, ZTE’s Pico BS for indoor coverage can support flexible subcarrier distribution and networking mode, FFR technology, adjacent signal measurement as well as frequency justification and optimization to minimize the interference in indoor coverage. These enhanced technologies effectively remedy the inherent deficiency of indoor conditions and bring great gain to coverage performance.

II. Adjustable solutions, rapid profit-making

The second difficulty faced by indoor coverage is how to solve the backhaul problem of R6 interface, and provide a cost-effective and fast deployment solution. Existing indoor transmission resources have two features: diversity and limitedness. Different operators have different indoor transmission resources, but to a specific application, the resource is mostly limited. For a fixed network operator, Ethernet or optical fiber resources are normally available in the building; for a cable operator, normally only cable resources are available in the building; for an emerging operator, wired resources are largely unavailable within the last mile, so as in the building; for a traditional 2G/3G mobile operator, it depends: in a better condition, some transmission resources such as FE and E1/T1 may be available, while in a worse condition, the transmission resources may be far from meeting WIMAX data transmission requirement.

For the difficulties mentioned above, ZTE has given a flexible and fast solution. For fixed network and cable operators, they can make the most of existing DSL, Ethernet, optical fiber and cable resources, with equipment directly integrating corresponding transmission interfaces thus achieving flexible deployment and capacity expansion. For some historical buildings or those that do not allow wall penetrating and rewiring, ZTE uses broadband power line (BPL) technology where ubiquitous power lines are used as plug-and-play transmission media, remarkably shortening network construction period, reducing construction cost, and allowing the operator to make profit rapidly. Besides the reduction of OPEX in the initial networking period, ZTE also helps the WiMAX operator to effectively reduce CAPEX through unified network management and charging.

III. Success stories in the high-end market

KT in South Korea, Sprint-Clearwire in USA and KDDI (UQC) in Japan are three major pioneers in WiMAX industry. Their development modes and successes serve as models for and are decisive to the whole WiMAX industry. From 2007, ZTE has successively entered Sprint in USA and UQC in Japan, starting its success stories in the high-end market.

The world’s first WiMAX commercial network by Sprint-Clearwire, a top operator in USA, will greatly influence global WiMAX industry. ZTE WiMAX’s indoor coverage system equipment have successfully entered into Sprint-Clearwire and is now working together with U.S. biggest enterprise solution pioneer to form the WiMAX enterprise solution industry model. On the Christmas eve of 2008, all test items of Pico BS were passed at Sprint Pico trial.

A major operator in Japan and a subsidiary of KDDI, UQC is responsible for the construction of Japan-wide WiMAX network, playing an important role in Japan’s post-3G network construction. ZTE’s WiMAX indoor solution smoothly entered the Field Trial stage and won complete recognition from UQC, making ZTE its WiMAX partner.

 

Due to the characteristics of WiMAX technology and service, WiMAX network is totally different from 2G/3G network using outdoor first and then indoor deployment mode. WiMAX can realize indoor and outdoor deployment simultaneously, or first starts from hotspot and indoor coverage then to the whole metropolitan area network, wide area network and even the nationwide network. In all, for WiMAX, indoor coverage is more important.

ZTE is willing to work with operators to technically break the restriction of traditional indoor deployment, and use feasible engineering deployment schemes to reduce indoor coverage cost, expedite networking and help operators to get ‘maximum’ success in ‘small’ indoor coverage world.