WiMAX Services and Interworking with 3GPP Based on IMS..

WiMAX Forum members are working with other industry groups, including the Wi-Fi Alliance, to enable seamless handoffs between multiple wireless standards, furthering the development of a cohesive wireless ecosystem. WiMAX Forum is also collaborating with groups like 3GPP on implementing IMS with WiMAX networks.

The 3GPP specifies the IP multimedia subsystem (IMS) to provide several kinds of multimedia services in UMTS Release 5 and later releases. Interworking at the service layer between 3GPP and WiMAX networks requires interworking between IMS functionality. By studying several interconnection scenarios and the main functionality of IMS, WiMAX can support different levels of services. Special attention is paid at the session negotiation level, using SIP, COPS/Go and Diameter protocols/interface to provide session negotiation with QoS and AAA (authentication authorization accounting) support.

Future mobile communication networks are evolving from traditional circuit-switched architecctures to an all-IP based structure. It is suggested that the mobile networks should be integrated by a high-bandwidth IP-based core network and a variety of wireless access technologies such as UMTS or WiMAX. Mobile terminals will be able to access different multimedia applications and advanced services while roaming across zones covered by different access technologies. Currently, 3GPP is developing a feasibility study on providing seamless service continuity between UMTS and WLAN.

Interworking between diffeernt networks can be viewed from different aspects. The most important aspect is the session negotiation level, which provides service continuity from the user perspective. At this level, the protocol used by 3GPP is Session Initiation Protocol (SIP), which is the foundation of the IMS architecture defined to support real-time multimedia services in future mobile networks.

The levels of convergence may be classified into convergence of service, network and technique. The goal is to share a service system based on interworking. Providing a uniform service experience for users, through a uniform service system, would enable customers to use different terminal devices to access heterogeneous networks, to access the same service, and to achieve common billing and session management. Service convergence is the first step of the convergence. Seamless roaming and handoff between different networks is the main problem. There are significant differences between the PHY technique of 3GPP and WiMAX.

• IMS Architecture

Within the UMTS core network, IMS is defined by the 3GPP as the component that provides support for multimedia services (e.g. voice and video) based on packet switching with QoS and the provision of AAA. The above figure shows a general view of IMS architecture. From this we can appreciate how the core network is organized in two networks: a signaling or control network and a data or transport network. The signaling network is composed of a set of call session control function nodes (CSCFs). They are signaling proxies whose task is to establish, modify and release media sessions with guaranteed QoS and AAA and charging support.

Note that user equipment (UE) gains access to the IMS via UMTS terrestrial radio access network (UTRAN), which is responsible for providing access for mobile stations and managing terminal mobility. SIP, COPS, and Diameter are the major protocols involved in this architecture.

• Interworking arthitecture and interworking level
  

1. Two interworking modes

There are two methods for WiMAX networks to interwork with other wireless networks: loose couple and tight couple. There is little difference between loose couple and existing networks; WiMAX utilizes the AAA server of 3GPP network, and data streams are not passed through the core network of 3GPP. This methods guarantees the independence of WiMAX network, however it results in high handover latency between two networks. Therefore, it is not suitable for real-time services.

In tight couple mode, the data streams of WiMAX must pass through the RNC and the core network of 3GPP, so each of the existing networks must modify their protocols, interfaces and services to meet the requirements of interworking. The BS of WiMAX connects with RNC of WCDMA or SGSN directly. The advantage of this mode is that it reduces the handoff latency and guarantees seamless handoff. If different operators own both 3G and WiMAX networks, the integration would be troublesome for the open of network interface.

2. Interworking levels

WiMAX is commonly used to transport IP packets. Thus 3GPP-WiMAX interworking should be built on the top of the IP protocol and not be limited to a specific WiMAX technology.

Different interconnection levels must be defined to represent different operational capabilities. These levels are suitable for either interworking mode.

Six interconnection levels between WLAN and 3GPP were taken into consideration., as well as the operational capabilities of each of them, based on the interconnection levels. The interworking is not limited to 3GPP and WLAN, but also includes the internetworking between 3GPP and other wireless access technologies based on IP. To maintain consistency, interworking with WiMAX networks must be based on the same model as shown in the following table.

3GPP has included the first three level s in Release 6, and the last two will be developed in future releases. The first level is the simplest and includes common billing (the customer receives just one bill for usage of both 3GPP and WiMAX services) and common customer care. It does not have any impact on either 3GPP or WiMAX architecture. The subscriber is charged on the same bill for usage of both 3GPP and WiMAX services. Customer care will be ensured independently of the connecting platform.

The second level (3GPP system-based access control and charging) includes the usage of the 3GPP access procedures (including authentication and authorization) for WiMAX users within the 3GPP domain. In addition, Wimax nodes use UMTS charging systems for charging data records generation. A subscriber may use the WiMAX Access network to access the Internet, for example, but AAA operations are handled by the 3GPP platform.

The third level extends the IMS services to the WiMAX. However, it is a matter of implementation as to whether all services are provided or just a subset of the services. This scenario lacks service continuity, so the user must re-establish the session in the new access network. Continuity is considered in this context as the ability to maintain an active service session when moving from one access network to another (e.g. between WiMAX and UTRAN) at the signaling level, without considering a transport level-related continuity issue like bandwidth or packet loss. Level 3 allows the operator to extend 3GPP system PS based services to the WiMAX network. In this scenario, an authenticated 3GPP subscriber can access 3GPP PS services through a WiMAX access network by interworking with its 3GPP PLMN (non roaming case) or with a visited 3GPP PLMN (roaming case).

The last three levels are not considered by the 3GPP in Release 6 and may be developed in future releases. The fourth level introduces service continuity, although the handover process may be perceptibel to the user (due to data losses or delays). The fifth scenario provides seamless continuity, with no noticeable service interruption greater than that perceived in intra-3GPP handovers.

3. QoS guarantee

Due to the differences in the network bandwidth, providing users with a constant level of service is not feasible. The goal of QoS guarantee is to offer suitabel quality of service in the given network, in accordance with user's QoS profiles and application require,ents. The QoS guarantee involves the task of mapping the QoS parameters from P-CSCF, GGSN, PDF, QoS negotiation, and the resource reservation methanism.

UMTS defines four classes of QoS services based on different application requirements: conversational, streaming, interactive, and background. WiMAX also defines four classes of QoS: UGS (unsolicited grant service), real-time polling service, non-real-time polling service and BE (best effort). According to the application scenario, QoS class mapping can be implemented according to the mapping relation mentioned according to the mapping relation. The conversational and streaming services of UMTS correspond to the UGS and rt-PS services in WiMAX. The interactive service can be mapped to nrt-PS and BE services in WiMAX in different application scenarios. However, the background service in UMTS has the same requirement and application scenario as the BE service in WiMAX.

QoS negotiation between session peers is performed using the SIP offer/answer model, in which each session peer offers its QoS capabilities using Session Description Protocol (SDP) descriptions in the message body.

The following figure shows the architecture of QoS-enabled interworking based on COPs.

The PCF communicates with the GGSN via the Go interface. It enables two modes of operation. In the push mode, the PCF initiates communication with the PEP and sends the decision to GGSN. In the pull mode, the GGSN initiates communication with the PCF to request a decision for a particular IP flow.

In summary, SIP is the key signaling protocol of IMS. Interworking between SIP elements of the WiMAX and CSCFs of the IMS is a key issue in reaching a high level of interworking between WiMAX and 3GPP networks. Here the overall architecture of the interworking based on IMS is represented, as well as special issues such as QoS guarantees are discussed.

The Competition between WiMAX & 3G and WiMAX Technology Development Trend..

As the fourth generation network, WiMAX system is expected to provide fixed wireless alternative to conventional DSL and Cable Internet.

The competition between WiMAX and 3G:

Before the December of 2005, WiMAX and 3G played their own roles. WiMAX focused on fixed wireless broadband, while 3G was planned to take place of 2G (GSM) mobile communicaiton. However after that, mobile communication of WiMAX standard: IEEE 802.16e came out which made the positions of WiMAX and 3G overlapping. Mobile WiMAX will firstly be used in laptops. Then the size and power will be further reduced in which way it can be used in PDA and more small size portable devices. Especially Mokia has announced that it will release WiMAX mobile phone in 2008 which shows that it is quite possible that Mobile WiMAX will be a new generation mobile communication, not only 3G in consideration.
At the same time, 3G is also trying to enhance its techniques to consolidate its domain. For example, 3G added HSDPA, HSUPA, etc. This increases the transmission speed in 3G data service and it encourages to use HSDPA in mobile devices other than mobile phones. Now there has already been HSDPA interface card for laptops. There is even built-in HSDPA when the devices are made. From this point of view, the competition between WiMAX and 3G has been quite obvious. Then which one will win the game?
As mentioned above, no matter it is WiMAX or 3G, the purpose and used techniques are identical. There is not much difference between them. In order to accelerate transmission, OFDM modulation must be used and MIMO technique must be used for sure. And the HARQ error control mechanism must be used to increase the spectrum efficience.
Except for the same improvement techniques, the implementation tempo between WiMAX and 3G is different. In all IP type and OFDM techniques, WiMAX is in front. Till now 3G still cannot realize all IP and it still has not implemented OFDM technique. As for MIMO and HARQ, 3G is in leading place. While for these two techniques, WiMAX has already included them at the end of 2005. So currently for pure ideal technology standard, WiMAX is superior to 3G.
However, the above is all the comparison of existing facts. The competition on technique has extended to the future promise. 3G field has already had many development plans, including HSDPA, HSPA+, HSOPA, 3GPP LTE, etc. In these future plans, OFDM technique is also introduced and the all IP architecture will also be used. While for WiMAX, after the completion of IEEE 802.16e, there is not very clear further technology plan.
But in 2007, WiMAX will have new behaviors which are mainly the proposals of .16j and .16m. IEEE 802.16j is the standard of Relay Station for Mobile WiMAX. The other one is a proposal for ITU-R. ITU-R is making standards taking the place of IMT-2000 and IMT-Advanced which belongs to the 4th generation mobile communication standard. WiMAX Forum expects that WiMAX techniques can appear in the new standard and at the same time make sure the copatibility of Mobile WiMAX and 4G new standard.
For IEEE 802.16j, the companies of Nortel, Fujitsu and Taiwan give a lot of contributions in the working group.

WiMAX (IEEE 802.16e) Advantages and Disadvantages!

What are the disadvantages or shortfalls of WiMAX network for a corporate network, requiring high capacity and total control over the network? Should Point to point be a better option?

Here we will talk something about disadvantages of WiMAX technology. Common misconception is that WiMAX can offer 70 Mbps in range of 70 miles (113 kilometers) with moving stations. But in practice situation is very different. It is true only in ideal circumstances with only one recipient. You could have with line-of-sight (optical visibility) speed of 10 Mbps at 10 kilometers. In urban enviroment (without optical visibility) users can have 10 Mbps at 2 kilometers. If users are moving, the speed can drop significantly. Bandwidth is shared between users in given radio sector, so if there are many users in one sector, they will have reduced speed. Users could have 2, 4, 6, 8, or 10 Mbps of shared bandwidth. The biggest disadvantage of WiMAX is still much bigger installation cost and also operational cost.So let's put on paper WiMAX advantages and disadvantages.

Advantages:

1) Single station can serve hundreds of users.

2) Much faster deployment of new users comparing to wired networks.

3) Speed of 10Mbps at 10 kilometers with line-of-sight.

4) It is standardized, and the same frequency equipment should work together.

Disadvantages:

1) Line of sight is needed for longer connections.

2) Weather conditions like rain could interrupt the signal.

3) Other wireless equipment could cause interference.

4) Multiplied frequncies are used.

5) WiMAX is very power intensive technology and requires strong electrical support.

6) Big installation and operational cost.

WiMAX also has other disadvantages. Firstly it is very expensive. Normally it is used for corporate solution which is hard and expensive to find frequency license! So its disadvantage is the spectral limitation, in other words limitation of wireless bandwidth. For use in high density areas, it is possible that the bandwidth may not be sufficient to cater to the needs of a large number of clients, driving the costs high. It has less QoS and the speed is up to 70Mbps.

So what will be the solution for higher bandwidth (BW) requirements to the corporate sector for their intra-net? No operator wants to give all his available BW at a sector to a customer. It will not be cost effective to them. Also this is about unlicensed band. Licensed frequencies are definitely hard and expensive to buy.

If we talk about one corporate network, we'd better use 5.8Ghz or other frequency and fixed network, but not WiMAX! It has much higher throughput than WiMAX, because you can use 10Mhz for channel bandwith. It is available!

May we can go for lisence free band 2.4Ghz, 5.8Ghz. For backhaul links it is better to use WiFi, which can reach high throughput (37Mbps) in Point-to-Point links. And it has low cost and ther is no paid cannon radioelectric (use ISM band).

Regardless of what the WiMAX forum is telling us, the 2.5Ghz spectrum is only functional in urban area where it can leverage reflective surfaces and where it can have good line of site in rural markets.The basic unspoken issue here is how ineffective the 2.5Ghz systems are when addressing any type foliage, those horrible little things called leaves have a tendancy to absorb all RF in that frequency, such as trees and bushes, which means that most of the East Coast. If you talk to the vendor engineers out of the reach of the marketing/sales types they will agree with the above. Wait until the FCC releases the 700Mhz spectrum and then WiAMAX makes a great deal of sense, unless the Cell Carriers win the spectrum and control it.

The last, but not lease, disadvantage of WiMAX technology is that true standards-based large mobile network deployments will probably not occur very soon. In the meantime, solutions based on EV-DO, HSDPA, and various proprietary technologies have already become available.

VoIP & IPTV Applications in WiMAX..

A fixed wireless solution not only offers competitive internet access, it can do the same for telephone service thus further bypassing the telephone company's copper wire network. Voice over Internet Protocol (VoIP) offers a wider range of voice services at reduced cost to subscribers and service providers alike. The diagram below illustrates a typical solution where a WiMAX service provider can obtain wholesale VoIP services (no need for the WiMAX service provider to install and operate a VoIP softswitch).

In residential markets, VoIP is a "must offer" service. Without the additional revenue per user , WiMAX does not offer a compelling reason to switch from other forms of residential broadband. When bundled with broadband internet access and IPTV, a WiMAX triple play becomes very attractive to residential subscribers. Given the QoS, security and reliability mechanisms built into WiMAX, sub-scribers will find WiMAX VoIP as good or better than voice services from the telephone company.

Another powerful application in WiMAX, is Internet Protocol Television (IPTV). IPTV enables a WiMAX service provider to offer the same programming as cable or satellite TV service providers. IPTV, depending on compression algorithms, requires at least 1 Mbps of bandwidth between the WMAX base station and the subscriber.

In addition to IPTV programming, the service provider can also offer a variety of video on demand (VoD) services. The subscriber can select programming a la carte for their television, both home and mobile, viewing needs. This may be more desirable to the sub-scriber as they pay only for what they want to watch as opposed to having to pay for doz-ens of channels they don't want to watch. IPTV over WiMAX also enables the service provider to offer local programming as well as revenue generating local advertising.

Television as Key Application for WiMAX..

Nowadays, various kinds of applications which need high data rate, have enter the field of WiMAX systems. This will definitely enrich the life of WiMAX users. MobiTV, Inc., the global leader in mobile and broadband television and music services, announced the Company has joined the WiMAX Forum and will be leading its Proof-of- Concept trial with the mobile WiMAX network that will span a number of Northern California cities. A representative of MobiTV has been assigned to co-chair the mobile WiMAX Application POC initiative within the forum's Applications Working Group.

"MobiTV is strongly committed to a significant and ongoing investment in research and technology development to support the very latest wireless network technologies, and our service integration with WiMAX is a true industry-first," said Dr. Phillip Alvelda, CEO, chairman and co-founder of MobiTV. "This technology is powerful two-way and interactive wireless technology that will transform the television industry."

"We are delighted to have MobiTV join the WiMAX Forum ecosystem as a key member helping drive the development of new multimedia applications that satisfy the demands for personal broadband services by consumers around the globe," said Ron Resnick, president of the WiMAX Forum. "MobiTV is a pioneer in delivering mobile television and other multimedia content, and we look forward to their contributions as the industry works to create content-rich and high-bandwidth mobile services that will be possible with mobile WiMAX Forum Certified(TM) products."

The Northern California based Proof of Concept network will provide an environment to evaluate a variety of mobile WiMAX applications, including mobile television broadcast, video-on-demand, navigation and general network access. A second Proof of Concept network will be deployed in Taipei, Taiwan under the direction of the National Taiwan University.

"We have been working in partnership with several leaders in the wireless and technology industries to support this new network solution at MobiTV," said Ray DeRenzo, vice president of business development for MobiTV. "By participating in the WiMAX Forum and helping lead the task group for mobile television, we are confident that MobiTV will contribute to the success of this standard, and more importantly the rapid deployment of this powerful technology."

WiMAX and mobile WiMAX are the latest extensions to MobiTV's portfolio of supported network technologies, with features designed to support all of the key components that make mobile television viable to consumers and carriers alike. Those key features and benefits of the MobiTV service for WiMAX and mobile WiMAX include:

• Smooth integration with, and natural extension to existing service infrastructure
• Efficient full-duplex bi-directional delivery with full transactional capabilities
• Superior data delivery performance for full-motion video (due to its advanced IP based architecture)
• Support for a combination of Unicast and Multicast delivery models for optimal network utilization
• Full interactivity; which includes m-commerce, voting and other capabilities consumers, carriers and the advertising community wants
• Targeted national, regional, and local advertising
• There are no channel line-up limitations with WiMAX
• Increased channel change speed
• Broad client device support including: mobile phones, PDAs, laptops, set top boxes and more (radios in mass market devices)
• Broad industry support and open-standards based
• Support for the rapid deployment of new applications and services (extensions to the MobiTV service) at a low incremental cost

All these properties make the Television a very promising application in WiMAX system.

Mobile WiMAX Technology and Application in Industry..

This time I will describe something about WiMAX application in industry and provide some analysis on WiMAX application progress. This part will also give some advantages and challenges for mobile WiMAX and analyze its uncertainty in China. There are mainly 3 aspects: the 3G license is till not distributed; it is harder to find the spectrum for mobile WiMAX than fixed WiMAX; the technology selection may effect the whole development of Telecommunication field in China.

• WiMAX standard series:

IEEE802.16 is also called IEEE Wireless MAN air interface standard, which works between 2~66GHz wireless spectrum. Because the provided wireless system coverage can reach as large as 50km, so 802.16 is mainly used in Metropolitan Area Network (MAN). Based on whether mobility is supported or not, 802.16 standard can be devided into fixed and mobile broadband wireless access airlink.

After the publish of 802.16e standard, the Mobile Multi-hop Relay task group of 802.16j became one of the groups with most participation in IEEE 802.16. Through mobile multi-hop relay technique, it can increase the transmission rate, extent coverage range, and achieve obtaining uniform data rate property for users in the coverage. This property is quite likely to fulfill the requirements of future 4G mobile communication technology. While IEEE 802.16 MMR SG is the only organization which puts this technique into standard. This attracts a lot of industry companies to join in and participate and it also became a new direction in 802.16 standard.

The signal of wireless network base station has shadow fading effect because of the coverage area. This makes the effective coverage shrink a lot. In order to make sure the the user signal is still continuous when there is serious shadow fading, signal relay is used to solve the problem.

The advantages of mobile multi-hop relay:

• Low cost: relay station doesn't need the support of wired-line backhaul which reduces the cost of building backhaul network greatly. And the complexity and cost of relay station is much lower than base station. So although the effect provided may not be as good as adding a cell, it is still very attractive to operator for its low cost and flexibility.

• Selective power amplification: Different from the traditional analog power amplifier to amplify all the received signal, relay station will make digital process for received signal and amplify the power depending on situation. Furthermore, because when the relay station receives the signals, the interfering signals have already been dealt with. So when relaying signals, all the power on the signals needed to be relayed. While the signals don't need to be relayed, interfering signals will not be relayed as well.

• Multi-hop increasing coverage area: many neighboring relay staions can relay signals to farther away areas.

Relay task group has decided that this standard should be realized under the condition without modifying mobile station. Then the mobile station may not be able to recoganize the existance of relay staion. This is also one of the difficulties.

Mobile WiMAX production speeds up:

WiMAX forum plays an important role in WiMAX market. The approval of this forum and other work decide the possible future development and application of WiMAX. Nowadays the main work has totally moved to wireless WiMAX and speeds up to put technology in market. The time of approval and whether it is successful has relation with when the WiMAX devices will be on the market.

The approval of fixed WiMAX devices has started from the beginning of 2006. While because the approval of mobile WiMAX was postponed, it can only start at the end of 2006.

After all, big Telecommunication vendors all around the world tend to develop 802.16e devices. Especially in China, ZTE and Huawei have already given up the plan to make fixed WiMAX devices. There are also some other big companies such as Alcatel, LG, Motorola, Nokia, Samsung, Siemens and Nortel, working hard on this system.

WiMAX Business Strategies..

As commercial applications of the IEEE’s 802.16 series of standards start to be deployed, fixed line, 3G network operators and WiMAX service provider specialists are seeking to understand which combinations of business models and deployment strategies will be viable.
Fixed line operators need to understand whether WiMAX can give them access to wireless broadband business and residential customers and the limitations and niches where mobile WiMAX can deliver broadband data services and perhaps voice and video services which are competitive with HSPA.
Operators of 3G networks who are launching HSPA need to understand the potential threat posed by WiMAX and whether to deploy WiMAX as an alternative to HSPA in regions where the demographics for building 3G networks were not favourable.
As the IEEE standard 802.16 does not define QoS, developers of WiMAX equipment and networks face severe hurdles in optimising a WiMAX network for delivery of non-data, time critical voice and video services and especially in security and equipment interoperability. Hence, there is an imperative to develop and demonstrate a class of service and security that is competitive with HSPA services.
Regulators have attempted to create a licensing environment that encourages competition between suppliers of WiMAX services whilst defining regions whose demographics are viable for commercial applications, thereby weakening the potential revenue for WiMAX license holders.
Further, the range of frequencies, licensed, unlicensed and lightly licensed, available to WiMAX service providers, creates significant barriers for handset manufacturers to produce devices that can utilise the diverse spectra used by different providers and that are competitive in terms of reliability, power requirements and cost-price with 3G/HSPA handsets. This represents another severe challenge to delivering mobile WiMAX services, especially for voice and video, which are competitive with 3G.
WiMAX faces current challenges from 3G/HSPA and UMTS-TDD and future threats from 3GPP’s LTE for MIMO-OFDM based UMTS wireless broadband which is already optimised for voice and video. Can WiMAX service providers sufficiently develop their markets and solve the QoS challenges to delivering voice and video in the face of these existing and evolving threats? It is still under discussion.