Difference between “WILLCOM WiMax” and Mobile WiMAX

“Only WILLCOM WiMax provides high throughput in urban regions.” this comment from a professional in casual chatting the other day surprised me. I was surprised not only because WILLCOM’s XGP system was recognized as WILLCOM WiMax here, but also because that WiMax was under suspicion by a professional of its assumed advantage of high throughput in downtown areas.

“WILLCOM WiMax”, this interesting saying might be indicating various meanings. We might as well get some outlook of this broadband wireless access of the next generation by taking a close look of its technique introduced below.

WiMAX , XGP and LTE share the same physical layer

Mobile WiMAX（here-in-after refer to as WiMAX）and XGP, together with W-CDMA’s successive technology LTE are as a matter of fact, similar technology. All of them are adopting a wireless transmitting technology called OFDMA（Orthogonal Frequency-Division Multiple Access）on their physical layer.（Despite that WiMAX has specified 5 physical layers with one of them as OFDMA, only OFDMA is in used as a matter of fact.） OFDMA, as a highly efficient transmission method to use frequency, enabled plural users to share simultaneous access of OFDM （Orthogonal Frequency-Division Multiplexing）, which is a toning method adopted in IEEE 802.11a/g/n and ADSL. The basic idea of the two methods is the same.

In an OFDM method, available band is divided by even smaller frequency called sub-carrier, high-speed communication is realized by sending signals to plural subcarriers. It is necessary to set intervals among listed subcarriers originally, in order to show the distribution of scales that each signal holds. Although, once a peak of one subcarrier can be listed up properly with the valley of a neighboring subcarrier, subcarriers then can narrowly divided without causing interference. OFDM realized high-speed communication by precisely squeezing subcarriers in frequency. By listing subcarriers up accurately, toning rate on time axle of a sign carried by individual subcarrier is kept low. This is an especially advantageous feature to carry out wireless telecommunication, in which radio interference happens naturally due to the delay and reflect of radio waves. Today, OFDM is regarded as the ultimate digital communication method that uses radio wave. Combining with MIMO technology, which enables the usage of plural antenna for both receiving and sending data, OFDM is becoming a de facto standard in digital communication world. Large scale integration under tremendous Fourier transform, which is necessary for the recovery and toning of OFDM, is also happening.

With this background, all next generation technology for BWA chose the direction of OFDM. UWB(Ultra-WideBand), which realized short distance super-speed wireless communication and ground digital broadcasting are using OFDM too. Instead of using weak radio wave to carry out narrow scale communication, wireless USB is developed and promotion of which started by making use of broadband for high-speed public communication.

XGP is almost the same with mobile WiMax

WILLCOM’s CEO, Mr. Hiroki Hirasawa proved “XGP adopted the same toning method with WiMax.” The company discussed internally of the possibility to adopt WiMax several years’ ago, but eventually made the decision to develop its independent technology.

Mobile WiMAX and XGP are different at subcarrier intervals and frame structure and both are difference on soft ware 。”This is the age that a wireless technology is identified with its software. There are various makers providing chips for WiMAX, but the majority of them provide chips dealing with hand ware. Therefore, XGP can adopt the chips in its own system as well.” Mr. Hirasawa said.

Last year, various tactics were seen to be used among telecom operators in Japan regarding the only two licenses to operate next generation BWA service. At that time, there used to be a strong voice calling for two licenses to be both given to WiMax operators. One argument of them was low procurement cost of its hardware. Regarded as the de facto international standard, WiMax was once regarded as the absolute winner in the cost war against XGP, which had no prospect for global procurement despite of being another recommended international standard by ITU-R.

But now that both are adopting OFDM method on physical layer and both can adopt similar hardware, procurement cost on cells or terminals should no longer stay as a problem. By this perspective, XGP can be regarded as a technology, which is a variation of mobile WiMax. The WILLCOM WiMax mentioned at the beginning of this article could just have the same meaning.

Mobile carriers towards LTE

Mobile WiMAX, XGP and LTE are competitors using similar technologies. It is hard to tell which will become the most popular and in which way the promotion can be carried out at best efficiency. Despite, it is true that the evolvement direction and original merits of each method, as well as their promotion scenario can be imagined clearer than before. (WILLCOM’s report titled XGP Business Deployment Based on XGP Establishing Plan and UQ Communication’s report titled Development towards BWA(WiMax) Service were promulgated on Apr. 18, 2008 respectively.)

First, let’s have a close look at LTE, which could be the easiest part. In Japan, President Onotera at KDDI indicated that LTE, instead of UMB（Ultra Mobile Broadband）has been chosen as the successive technology for CDMA2000 during an interview on April 24, which revealed the future direction of the three mobile carriers. In the U.S., situation is to be similar as its CDMA2000 operator Verizon Wireless announced the adoption of LTE by the end of last year. In Europe, Alcatel Lucent just formed a joint venture with NEC to get ready for a big scale development system.

There are several reasons that mobile carriers have chosen LTE over WiMax. One of them is the easy support of voice communication. LTE can provide voice service via VoIP as well as through conventional network via circuit. Besides, hardware like Flexi Multimode, which are provided by Nokia and Siemens to be used in LTE corresponding base stations, are able to support W-CDMA／HSPA／LTE simultaneously. The product, which makes it easier for a base station to evolve phase by phase, can be very attractive to carriers.

Adopting the reasonable form of progress from W-CDMA and HSPA to LTE, under the name of evolution, can be a wise upgrade path for the existing carriers. Nokia and Siemens argued that due to LTE’s feature of low latency, new users, such as those game players with high request of real time can be developed. Besides, due to the demerit of high power consumption that OFDM has, LTE is considering the adopting of FDMA instead of OFDM to expand the duration of terminal batteries.

The prospect of Mobile WiMax is obscure. WiMAX Forum has announced the target to grow 133 million users by 2012, but the way towards the target isn’t flat.

In the U.S., Sprint, Nextel and ClearWire have talked about building a national WiMax network, but the deployment was retreated all around in November 2007, which surprised the whole industry.

Mobile WiMAX camp, starting from Intel, hasn’t changed its plan to carry WiMax on chips, mobile PCs and MID (mobile internet devices), even if the rise of LTE has already brought about the age of next generation, in which mobile is not combined with devices such as mobile phone, PC and MID.

Considering the taste of consumers and vendor’s the supply system, terminals shall stay as something resembles mobile phones by common knowledge. Just like the fact that IP phone wasn’t expanded at expected speed in fixed-line world, in the world of mobile phone, we don’t expect the quick popularization of VoIP and the overnight spread of next generation terminals even when high-speed data communication becomes possible. In a certain period, we will continue using handset with similar appearance to traditional ones and similar voice functions to connect ourselves to a world with “somehow faster web access”.

Difference between XGP and Mobile WiMax

Regarding data communication through note PC and MID, mobile WiMax and XGP are more prospective. Despite of the fact that both systems use OFDM technology, the design of base stations and the structure of MAC layer are completely different.

The biggest difference lies with the density and installation method of base stations.

According to Ms. Hirasawa, the decision that WILLCOM abandoned WiMax to develop its own system is made on a conclusion of research, which indicated that WiMax might not meet the need for high-speed data communication in downtown area. Conventional systems, as well as WiMax and LTE requested accurate deployment of base stations in hexagon to avoid radio interference among cells.

While in case of PHS and XGP, ADC (automatic decentralized control) function is adopted to allot proper frequency resource that doesn’t result in interference between each other. “Cells can be established at favorite pace and location without considering the way to deploy and construct them.” Mr. Hirasawa Said.

For example, WILLCOM has one hundred antennas erected in an area with 500 meter in radius in downtown Tokyo. While according to Mr. Toshikazu Iriumi, Head of Network Technology Department at UQ Communications revealed that WiMAX service expects to use one cell to cover an area with 750 meter in radium in downtown. The difference is obvious. In a mobile WiMax system, each cell is supposed to realize a bandwidth of 240Mbps. And the theoretic throughput will not be realized under the user environment since this is the bandwidth shared by all terminals in the coverage of 750 meter in radius. This is also the same in case of LTE, as the number of terminals under one cell increase, the deterioration of throughput is unavoidable no matter how quick the transmission can be under one cell to one user situation. Despite that there is such a technology called Space Multiplex to virtually divide cells with improved directivity of sending waves, basically telecommunication through radio waves is just like entering a room and make speech one by one. Comparing to the method to jostle many people into one huge room, to arrange the same number of people in separate small rooms gives each people longer hours to speak.

Willcom system is called micro system, with each cell covering a narrow area. This micro cell system is known as PHS, which was firstly used as cordless extension of a fixed circuit in office and family environment. The system gives out low radio wave due to small cells. The system has also adopted ADC to realize the flexible installation of base stations earlier than other systems. Both features are advantageous conditions for next generation wireless communication.

According to WILLCOM, which has been providing data communication service till today, about 80% of the total traffic came from Tokyo, Nagoya, Osaka and capital cities of respective prefectures. In another word, majority of the need for data service comes from urban dwellers. More specifically, the peak request happens at area with cluster of people, such as Shinjuku and Otemati in Tokyo.

You might not be able to detect the big difference between WiMax and XGP if mobile is only used to send mail and look for information like the way it was used now.　But just as broadband has once changed the concept of the world completely, wireless broadband might be able to change the definition of telecom one day. One can watch movie like reading a book today wherever he or she goes, unexpected service can be provided by MVNO. What will happen if Nintendo connects game machine to a WAN telecom device? Or, what service will it be to combine a video camera with a WAN telecom device? With WAN telecom device, isn’t it that even functions like security camera can be fit into simple network construction? How about a streamlined MP3 without storage?

Just think about the broadband used with desk-top now could be used on a mobile device, and then you could never misread the impact of mobile broadband. WILLCOM and UQ Communications are working on the agreement with MVNO now. They are getting business ideas from unexpected parties other than ISP and PC makers as well.

PHS can not become a Galapagos market

Despite that PHS has made some achievement in introducing itself within Asia, including places like China and Taiwan area, it is more often recognized as a Japan-generated local specification. So is XGP.

Regarding the globalization plan of XGP, Mr. Hirasawa said, “No other way but to show its true power. We just believe in its technical advantages.” After all, the comment revealed some worries, because technological advantage is only one of the many factors to market success. Even if the new terminals designed with delicacy are to sweep over the global market in 2009, they could be only corresponding to WiMax.

Despite that PHS can make use of WiMax chips by changing firmware or doing patch work at certain degree, problems could still exist with politics, regulations and other common recognition among businesses. In this sense, WiMax is on a much more advantageous position concerning its impetus on global market.

Although, on the other hand, in the battle over different communication methods in this software wireless age, if terminals, in particular, become no longer as important as it was before, XGP should have a better chance to thrive. On Japanese market, dual-mode terminals for both mobile WiMAX and XGP systems can enable the selection of network on users’ will. Once XGP convinced Japanese users of its superiority, it can be marketed worldwide. Then, can Asia, a place with dense population be the following next marketing target? One the contrary, if there is no reason to choose XGP, users might choose WiMax, which makes roaming easy. Either way, XGP corresponding terminal will not deserve the criticism as a Japanese product isolated from the global market, or a Galapagos product, as it is comparatively easy to fit chips that correspond to both systems in the terminals. Even mobile phone and PHS terminals found a way to co-exist on the market, why should mobile WiMax fail to co-exist with XGP? Owning to the high-quality provided in voice service and high-compatibility in data communication, PHS has its own fans. In the same way, XGP has its appeal to businessman and users in IT industry. In case of XGP, those base stations which are in use now can be attractions to users. Even if an existing cell station hasn’t been modified to carry out XGP service, voice and data communication with conventional PHS will always be possible since the exchangeability is always there.

The writer believes that micro cell method will be looked over again once XGP meets its success. In the world of mobile, Mini cell station such as Femto Cell should not be mentioned only in occasions that a carrier needs to expand coverage at area that radio wave didn’t reach. It should also be considered when there is need to improve efficiency of radio wave. Just like OFDM, which has already become the inevitable choice of time, XGP technology, which adopted micro cell method and Space Multiplex might have chance to become another choice of the time.

Of course, the result depends on the market, which combines the reflection from users, makers and service providers. The deciding factors of a wireless communication method not only include transmission speed and installation cost. Power consumption, stability during high-speed movement, latency and constant performance during handover are also the factors to evaluate the system. We can’t decide which method is superior or how advantageous a method is unless it is put into various applications in real operation. Therefore, I’d like to focus first on what kind of answer the market will give once mobile WiMax and XGP start service in 2009.

source file (2008-09-19)


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