Research on WiMAX Network Application Scheme Based on IEEE 802.16e Technology

The IEEE 802.16 working group recently released the wireless metropolitan area network standards IEEE 802.16-2004 and IEEE 802.16e that support fixed and mobile broadband wireless access. Both IEEE 802.16-2004 and IEEE 802.16e are specifications for the physical layer and media access layer. Among them, the wireless metropolitan area network standard IEEE 802.16-2004 is a fixed broadband wireless access specification formulated by IEEE 802, and IEEE 802.16e is a standard for IEEE 802.16- Supplementary and revised version of 2004, with the expectation that on the basis of IEEE 802.16-2004, it is expected to provide user stations with functions and services capable of moving at vehicle speeds.

The IEEE 802.16 working group recently released the wireless metropolitan area network standards IEEE 802.16-2004 and IEEE 802.16e that support fixed and mobile broadband wireless access. Both IEEE 802.16-2004 and IEEE 802.16e are specifications for the physical layer and media access layer. Among them, the wireless metropolitan area network standard IEEE 802.16-2004 is a fixed broadband wireless access specification formulated by IEEE 802, and IEEE 802.16e is a standard for IEEE 802.16- Supplementary and revised version of 2004, with the expectation that on the basis of IEEE 802.16-2004, it is expected to provide user stations with functions and services capable of moving at vehicle speeds. In order to accelerate the application of IEEE 802.16 technology and the formation of the industry chain, by defining the frequency band, application scenarios and interoperability of IEEE 802.16 technology application, the industrial organization WiMAx Forum further provides the capability of interconnection and interoperability based on IEEE 802.16 technology, and Network resource management and control functions and testing specifications.

As IEEE 802.16e potentially supports the mobile capability of wireless broadband and the active promotion of the WiMAX Forum, the application of WiMAX mobile networks based on IEEE 802.16 is becoming a hot topic of discussion in the industry. IEEE 802.16m was selected as one of the candidates for the next-generation wireless communication standard (IMT-ad-vanced). Compared with IEEE 802.16e, in order to meet the performance requirements of IMT-2000 and IMT-advanced, IEEE 802.16m emphasized the addition Some enhanced physical layer functions, such as Relay, multicast, power control and multi-antenna technology, but in terms of supporting mobility and interconnection with IP technology, WiMAX networks based on IEEE 802.16m and IEEE 802.16e are not obvious The difference. This article will first study the mobile service capabilities of IEEE 802.16e, and then focus on the IP-based mobile WiMAX network solution, which can also be used as a future network application solution based on IEEE 802.16m technology.

1. IEEE 802.16e supports mobile* capability

On the basis of 1EEE 802.16-2004, IEEE 802.16e is mainly extended at the physical layer and media access layer to support multi-user communication and network mobility* capabilities. The following is an analysis of its enhanced functions based on the physical layer and the MAC layer.

1.1 Physical layer enhancements and features of IEEE 802.16e

Orthogonal frequency division multiplexing (OFDM) technology is a sound communication technology for effective information transmission in channels. This technology uses multiple parallel sub-carriers (sub-carrier frequencies) that transmit low-rate data to achieve high-data-rate communication. The advantage of OFDM technology also lies in its ease of simplifying the channel equalization process, and supports multi-user channel allocation and link adaptation in the time domain and frequency domain, thereby further improving the spectrum utilization of the OFDM system. Compared with OFDM, the use of OFDMA can bring more flexibility, that is, according to different channel characteristics and data volume requirements, channel and power resources are allocated through sub-channel diversity, thereby more effectively improving the efficiency of resource allocation.

IEEE 802.16e further adopts scalable OFDMA (sealable orthogonal freqtaency division mulTIplexing access, SOFDMA). Under a constant sub-carrier frequency, by extending the FFT size, the system can easily adapt to different channel bandwidths. For example, if the sub-carrier frequency is set to 10.94 kHz, by adjusting the FFT size, the bandwidth of 1.25 to 20 MHz can be flexibly supported.

The scalable OFDMA system adopts diversity and proximity methods to realize sub-carrier replacement or dispersion in sub-channels. Among them, the purpose of diversity is to randomly combine sub-carriers into sub-channels to provide frequency diversity and average inter-cell interference. Typical diversity replacement methods include downlink FUSC (fully used subcarrier), downlink PUSC (parTIally used subcarrier) and uplink PUSC. Figure 1 (a) and Figure 1 (b) respectively enumerate the sub-carrier distribution of downlink PUSC and uplink PUSC. The downlink PUSC adopts a cluster structure, that is, a string is composed of appropriate subcarriers in each pair of OFDM symbols in the downlink PUSC, and each OFDM symbol includes 14 continuous subcarriers for data and pilot. The uplink PUSC adopts a chip (TIle) structure, 12 sub-carriers form a chip, and 6 chips are reorganized and replaced to form a time slot. That is, one slot includes 48 data and 24 pilot subcarriers distributed in 3 OFDM symbols. Among them, the data subcarrier is used for data transmission, and the pilot (pilot) subcarrier is used for estimation and synchronization.

Research on WiMAX Network Application Scheme Based on IEEE 802.16e Technology

The study of proximity permutation includes downlink AMC and uplink AMC, which can support multi-user diversity in the OFDM (A) system, which is more convenient for link adaptation processing. Among them, consecutive sub-carriers from the same OFDM symbol form a bin. A slot of AMC is defined as a combination of multiple bins. The combination methods are:[6 bins, 1 symbol][3 bins , 2 symbols][2 bins, 3 symbols][1 bin, 6 symbols]. AMC replacement mode subcarrier diversity replacement is more suitable for mobile systems, while continuous replacement mode is suitable for fixed, nomadic and low-speed mobile environments.

1.2 MAC layer enhancements and features of IEEE 802.16e

The mobile* capability of IEEE 802.16e is more reflected in the improvement of the MAC layer. The key MAC layer technologies provided include mobile* support, handover, and power-saving modes.

1.2.1 Mobility support for 802.16e

In order to support handover and other mobility*, IEEE 802.16 provides functions such as acquisition of network topology, scanning of target base stations, correlation, ranging, and cell reselection at the MAC layer. The mobile station scans neighboring base stations to determine a new diversity set. The scanning step includes; identifying a suitable base station; synchronizing with its downlink transmission and estimating its channel quality; ranging to enable the mobile station to complete the synchronization process with a certain base station. Ranging can be based on conflict and non-conflict. The non-conflict-based ranging provides a faster and reliable synchronization method, but at the cost of resources; correlation enables the mobile station to record the number of successful scanning and ranging of the base station of the diversity set, accelerating the transfer of the mobile station’s business To the target base station; and the neighbor list broadcast enables the base station to generate a neighbor list with the aid of the network site back-haul (back-haul) to support the handover service of the mobile station. The list information is in the message element “handoffNeighbor preference” of MOB_NBR_ADV. The base station periodically sends the neighbor list, and each base station maintains the MAC address mapping table and its index of the neighbor base station.

1.2.2 MAC layer switching capability

Hard handover is a mode that must be supported in IEEE 802.16e. Under hard handover, the high-level connection and the convergence sub-layer data of the MAC layer can be buffered and then seamlessly transferred to the target base station. Macro diversity handover (MDHO) and fast base station handover (FBSS) are enhanced optional handover modes. MDHO supports both uplink and downlink transmissions. It allows the mobile station to simultaneously transmit and receive transmissions with multiple base stations in the diversity set. The difference between FBSS and MDHO is that although the mobile station synchronizes with all candidate base stations in FBSS, it only communicates with a central base station. Hard handover, MDHO and FBSS technologies provide mobile support at different application levels. MDHO and FBSS can reduce handover delay and support effective resource and network management.

2. WiMAX dull network reference model

Based on IEEE 802.16 technology, the WiMAX Forum provides a network architecture that supports mobility to support mobile services above the MAC layer, as well as roaming and handover services at different network nodes.

The network reference model (NRM) shown in Figure 2 includes the logical functional entities of the access service network (ASN) and the connection service network (CSN). ASN is composed of one or more base stations and one or more ASN-GW (ASN gateway). It is a complete set of network functions, providing such as radio resource management (RRM), data forwarding, data integrity, key distribution, etc. The key function is to provide wireless access services to WiMAX users. Among them, the RRM function can be completed in the base station or ASN-GW. A node that completes this function can request other base stations to obtain the required information, and use this information to help determine candidate base stations to meet the needs of processing such as handover and load balancing. In key distribution, a pairwise master key (PMK) is calculated on the mobile station side and forwarded to the central authority in the ASN-GW. PMK and base station identifier are used together to generate authentication password (authenTIcation key, AK). When switching to the target base station, a new AK is required. Using distributed computing to support the generation of a new AK corresponding to the target base station in the ASN-GW, and send it to the target base station as handover information. This processing method can avoid performing the user authentication process at each handover, thereby reducing processing delay. CSN needs to provide WiMAX users with core business capabilities such as AAA and DHCP servers and databases. Different logical entities complete interoperability through various reference points (R1, R4, R5, etc.).

Research on WiMAX Network Application Scheme Based on IEEE 802.16e Technology

Research 3. IP-based mobile WiMAX network

It can be seen from the above analysis that IEEE 802.16e provides the ability to support mobility in the physical layer and the MAC layer, and the WiMAX Forum provides network interfaces and interconnection models above the MAC layer, including the provision of mobility management and resources. Management and AAA service capabilities. The following research is based on mobile network services based on mobile IP and WiMAX technology.

3.1 IP-based mobile WiMAX application model

Figure 3 shows the IP-based mobile WiMAX application model. The model includes the following functions: Provides the ability to logically divide the above steps and IP-based routing and connection management to support different application scenarios in islands and interconnection modes; supports multiple NSPs to share 1 NAP ASN network; supports 1 NSP provides services to multiple ASNs to manage one or more NAPs; supports mobile stations or SSs to discover and select access NSPs; supports NAPs using one or more ASN network topologies; supports access to different operators through interconnection Services; Provide open reference points in different groups of network entities, enabling different operators to implement different combinations of functions based on different entities. In order to realize IP mobile network management, the network should support mobile IP technology, that is, CSN needs to provide WiMAX users with capabilities including IP connection services, network switching, and system roaming.

3.2 Mobile IP technology

Mobile IP allows the mobile station to change its access point for accessing the Internet without changing its IP address, that is, it allows the mobile station to maintain the transmission and high-level connection when performing handover. The packet directed to the mobile station is first routed to the home network, and the home agent of the mobile station intercepts the packet and tunnels it to the current address that the mobile station often reports. When the NWG group of the WiMAX Forum allows 2 types of mobile solutions. Using the user MIP (Client MIP) solution, traditional mobile IP signaling can be used to complete mobility management. In proxy MIP (proxyMIP), the network side can initiate a mobile IP client process, and the virtual client completes the mobile IP signaling process.

3.3 System Handover and Roaming Service of WiMAX Network Application Model The WiMAX application model can support intra-system handover in the same gateway (ASN-GW), handover between different gateways, and roaming service. The following is a further analysis in conjunction with the IEEE 802.16e protocol.

3.3.1 Intra-ASN system handover

According to the physical layer and MAC layer capabilities provided by IEEE 802.16e and the WiMAX network reference model, handover in the Intra-ASN system is completed. Among them, the R8 interface (not shown in Figure 3) can be used to implement communication between base stations. In OFDMA system, the switch can be decided according to the carrier-to-interference ratio (CINR) parameter. In various handover types, continuous CINR measurement is necessary. In compliance with the relevant provisions of the IEEE 802.16e protocol, the system can make the mobile station periodically scan the neighboring cell base stations through scan request and response messages, trigger neighbor scans and initiate handover. Including the following steps:

Research on WiMAX network application scheme based on IEEE 802.16e technology (1) When the mobile station detects that the CINR signal of the serving base station is lower than the rejection threshold (H_Delete_Threshold), it can initiate a neighbor scan to measure the CINR value of the neighbor base station. When the mobile station detects that the CINR value of a neighboring cell base station is higher than the signal increase threshold (H_Add Threshold) of the serving base station, it initiates a handover request.

(2) Both the base station and the mobile station can decide the process of selecting the target base station. The mobile station can select the target base station through scanning to complete the handover process; the mobile station can also feed back the measurement result to the serving base station through the MOB_mobile station SHO_REQ message, and the serving base station determines the final selected target base station.

3.3.2 Handover between Inter-ASN systems

With the help of mobile IP technology, MIP-based and proxy-based MIP mobility management methods are used to complete cross-ASN-GW handover. In the MIP-based handover mode, the MIP client resides in the mobile station, and the mobile station implements the MIP function, and the cross-ASN-GW handover is initiated by the network side. It includes the following steps:

Research on WiMAX Network Application Scheme Based on IEEE 802.16e Technology

(1) The trigger condition of the handover occurs;

(2) ASN-GW sends an agent announcement message to the mobile station;

(3) After receiving the agent announcement with the new care-of address (CoA), the mobile station sends it to the home network agent (HA). MIP registration message to ensure the continuity of the mobile station session;

(4) The MIP registration message is forwarded to the HA, and the HA returns the MIP registration response, and the currently serving visited network agent (FA) will finally return the MIP registration response to the mobile station.

In the proxy MIP-based switching mode, the ASN-GW assumes the proxy MIP function. The MIP client resides on the ASN-GW, and the ASN-GW implements the MIP function for the mobile station agent. In the proxy MIP mode, the ASN-GW obtains the relevant information required for MIP registration from the AAA server during the authentication phase, including the DHCP service address, generating the security information for the authentication extension, etc. The cross-ASN-GW handover processing is for the mobile station transparent.

It includes the following steps:

(1) The serving ASN-GW notifies the target ASN-GW to establish a new MIP session;

(2) The target ASN-GW sends MIP registration to HA;

(3) A new MIP session is established. After the MIP is successfully registered, the HA will send the subsequent forward messages of the mobile station to the target ASN-GW;

(4) Trigger the target ASN-GW to establish a tunnel with the base station;

(5) A new Intra-ASN tunnel relationship is established between the target ASN-GW and the base station.

3.3.3 Roaming

The roaming function enables WiMAX users to use network services including authentication and billing provided by the system within the coverage area of ​​the visited network, thereby providing users with a wide range of coverage and business access. WiMAX as shown in Figure 4 supports roaming. ASN provides wireless access. The V-CSN of the visited NSP provides users with functions such as Internet access and AAA proxy. The H-CSN of the home NSP provides users with functions such as Internet access, user authentication, authorization, and accounting. Roaming users can access the Internet network through V-CSN or H-CSN. Main process steps:

Research on WiMAX Network Application Scheme Based on IEEE 802.16e Technology

(1) The mobile station is connected to the network;

(2) The H-CSN of the home NSP performs user/equipment authentication and IP address allocation to the mobile station;

(3) Optionally, if the user supports standard MIP or proxy MIP services, the system will also use standard MIP or proxy MIP to establish a MIP session for the user;

(4) Users can connect to the Internet through V-CSN;

(5) If there is a mandatory tunnel requirement, then the user will access the Internet network through H-CSN.

When a user signs up as a WiMAX user who supports roaming and supports roaming between his home network and the visited network, the user can access the WiMAX system on the visited network regardless of whether the user uses nomadic, portable or fully mobile services. In order to use the services provided by the system.

4. Conclusion

This article comprehensively studies the service capabilities that support mobility in the IEEE 802.16e technical specifications and WiMAX network structure, and further provides an application model of IP-based mobile WiMAX networks, which provides a way for the application of IEEE 802.16 technology and the formation of the industry chain. refer to. The study further found that although IEEE 802.16e provides a series of mobile service capabilities at the physical and MAC layers of WiMAX networks, and WiMAX provides mobility management, authentication and network interfaces, the WiMAx Forum has not been perfected and optimized to support interconnected mobility. Management and resource management, and network applications based on mobile IP applications are still under study, and the mobile service management of WiMAX networks under the optimization of network resources will be further studied.

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