Networking technology of WiAMX in Europe

HIPERLAN/2 is a new generation wireless LAN technical standard developed by ETSI in Europe to meet the needs of future Internet access and broadband multimedia data services. It works in the frequency band of 5GHz and uses OFDM as the physical layer, so it can effectively resist multipath interference and improve the data rate. In addition, because they use the same physical layer as 802. 1 1a, they can share some of the same components, thus greatly reducing the system cost.

This paper briefly introduces the characteristics and protocol stack structure of HiperLAN/2.

Keywords: wireless LAN HiperLAN/2

1, background

So far, wireless networks are more or less similar to cellular networks based on different standards, such as GSM and AMPS. They are mainly used to support voice services, although some also support data services at a lower rate. Wireless data services that can meet the requirements of Internet access are being developed. In the LAN environment, many vendors provide wireless LAN products based on 802. 1 1, which can provide bandwidth from 1mbit per second to1mbit per second. As the price drops, WLAN will become an alternative to fixed Ethernet access. In order to meet the needs of the future network, the combination technology of WLAN and cellular network is developing. These requirements include supporting QOS and security, supporting the switching between LAN and WAN, and meeting the high bandwidth of data and video applications. This paper will introduce the next generation wireless LAN technology HiperLAN/2.

2.iperLAN/2 Network

The mobile terminal (MT) can communicate with the access point through the air interface defined by HiperLAN/2. Two mobile terminals (MT) can also communicate directly. Users of MT can move freely in HiperLAN/2 network, which can ensure that users of MT can obtain the best possible transmission performance. After accessing HiperLAN/2 network, MT only communicates with one access point (AP) at a time. The AP ensures the automatic configuration of the wireless network and considers the change of the wireless network topology.

Characteristics of 3.HiperLAN/2 Network

The general characteristics of HiperLAN/2 technology are:

3. 1 high-speed transmission

HiperLAN/2 has a high transmission rate, with the physical layer reaching 54M bits and the Layer 3 reaching 25mbits per second. HiperLAN/2 uses a modular method called orthogonal frequency digital multiplexing (OFDM) to transmit analog signals. OFDM is very effective in time-sharing environment. The new MAC protocol based on physical layer adopts the method of dynamic time division multiplexing, which can make the most effective use of resources.

3.2 Connection-oriented mechanism

In HiperLAN/2 network, data is transmitted through the connection established between MT and AP. Connections over the air interface are time division multiplexed. Hielan/2 has two types of connections: point-to-point connection and point-to-multipoint connection. Point-to-point is two-way, and point-to-multipoint is from AP to MT.

3.3 support QOS

HiperLAN/2 can directly support QOS because of its connection-oriented characteristics. Each connection can be assigned a certain QOS, such as bandwidth, delay, delay jitter, bit error rate and so on. This high transmission rate and QOS support will facilitate the simultaneous transmission of many different types of data streams, such as video, voice and data.

3.4 Automatic frequency allocation

In HiperLAN/2 network, there is no need for manual frequency compilation like cellular network. The wireless access point AP of HiperLAN/2 can automatically select the wireless channel for data transmission within its coverage. AP monitors neighboring APs and other wireless resources, and selects appropriate wireless channels according to the channels used by other APs, thus reducing interference.

3.5 Support security

HiperLAN/2 network supports authentication and encryption. AP and MT can authenticate each other, thus ensuring authorized access to the network (from the perspective of AP) or access to effective network operators (from the perspective of MT). Authentication requires supporting functions, which will not be within the scope of HiperLAN/2 network. Connected user data can also be protected by encryption to prevent eavesdropping.

3.6 Support mobility

MT will ensure that it sends and receives data from the nearest AP. More precisely, MT uses the AP with the best wireless signal by measuring the signal-to-noise ratio. Therefore, with the movement of MT, when MT detects that there is an AP with better wireless transmission performance than the currently used AP, MT will request to switch to a new AP, and all established connections will be transferred to the new AP, while MT is still on the HiperLAN/2 network and can continue communication. Some packets may be lost during handover. If MT moves out of network coverage for a period of time, MT will lose all contact with NiperLAN/2 network and all connections will be released.

3.7 Network and application independence

The protocol stack of HIPERLAN/2 has great flexibility and can adapt to many fixed network types. Therefore, HIPERLAN/2 network can be used as both the wireless access subnet of switched Ethernet and the access network of the third generation cellular network, and this access is completely transparent to users above the network layer. At present, any application on fixed network can run on HIPERLAN/2 network. In contrast, a series of protocols of IEEE802. 1 1 can only be supported by Ethernet, so this high flexibility is also the characteristic of HIPERLAN/2.

3.8 energy saving

In HIPERLAN/2 network, the mechanism of energy-saving management is based on the energy-saving request initiated by mt. At any time, MT can request AP to enter a low-power state or sleep period. According to different requirements, such as shorter waiting time or lower power, different sleep periods can be adopted.

4.HIPERLAN/2's protocol stack structure.

The protocol stack is divided into a control plane part and a user plane part. The user plane includes the function of transmitting data on the established connection, and the control plane includes three functions: establishing connection, releasing connection and managing connection. HIPERLAN/2 has three basic layers: physical layer, data link layer and convergence layer.

4. 1 physical layer

As mentioned above, the physical layer of HIPERLAN/2 adopts OFDM technology to effectively combat the strong multipath interference in time-dispersive channels. It uses 52 subcarriers, of which 48 subcarriers send actual user data, and the other 4 subcarriers send pilot sequences for phase tracking during correlated reception. The channel interval is 20MHz and the guard interval is 800ns, which is enough to resist the delay spread of 250ns and is also enough for most application environments. For some small indoor application environments, a shorter protection interval, such as 400ns, can be used to obtain higher transmission efficiency.

Another feature of HIPERLAN/2 physical layer is that there are many modulation and coding methods to choose from. In this way, different methods can be adopted according to different application environment restrictions and performance requirements. The modulation methods of OFDM single subcarrier can be BPSK, QPSK, 16QAM and 64QAM. Generally, convolutional coding is used for forward error correction, and the code rate is 1/2, and the constraint length is 7. However, truncation technology can increase the code rate to 9/ 16 or 3/4.

4.2 Data Link Control Layer

The data link control layer consists of data links between an AP and multiple mt, and the functions of logical link control include media access, data transmission and connection control. Therefore, the data link layer includes the following sublayers:-Media Access Control Protocol-Error Control Protocol-Radio Link Control Protocol (RLC) for connection control (DCC) of signaling entity DLC, and radio resource control for joint control function.

4.2. 1 Media Access Control Sublayer

The MAC sublayer of HIPERLAN/2 adopts the centralized management of AP, which is responsible for controlling the time slots occupied by MT in a MAC frame and informing the corresponding MT ... that the air interface is based on time division duplex (TDD) and dynamic time division multiplexing (TDMA). MAC frame is the interface between physical layer and DLC layer. In a MAC frame, uplink and downlink communication can be synchronized, and the time slots of uplink and downlink can be dynamically allocated as needed. The basic MAC frame is a fixed length of 2ms, including broadcast control, frame control, access control, uplink and downlink data and random access. All data should be transmitted between AP and MT through dedicated time slots, except the time slots that allow contention for random access channels. Except for the fixed broadcast control channel, other domains are dynamically adjusted according to the current traffic situation.

The EC is mainly based on ARQ strategy. Forward error correction is a supplement to EC. ARQ strategy is based on selective retransmission mechanism. This requires a careful transmission window at the receiving end and the initiating end. Therefore, the receiver must inform the initiator (1) of the sequence number (2) of all received messages, and these messages are incorrect. In addition, the initiator may discard some messages because they exceed the maximum length of time.

Signal and control

The radio link control protocol provides transmission services for signaling entities: joint control function (ACF), radio resource control function and DLC user connection control (DCC). These four entities constitute the control plane of DLC signaling exchange between AP and MT, and joint control function (ACF): A MT wants to communicate with AP, and must first join the AP. The main functions are association, disassociation, authentication, encryption and encryption keyword management. Radio resource control function (RRC): RRC is mainly used to monitor and effectively use available frequency resources. The main functions are: dynamic channel selection, mobile terminal activity process, mobile terminal absence process, power saving function, transmission power control and switching. User Connection Control (DCC): Manage DLC connection control, connection establishment process, connection management, connection release, multicast and broadcasting. 4.3 convergence layer convergence layer has two main functions: adapting high-level service requests to services provided by DLC, and changing high-level packets into fixed-length packets used by DLC. The division and reorganization of fixed-length DLC SDU is the key technology to standardize and realize DLC layer and physical layer. The structure of. CL makes HIPERlan/2 suitable for wireless channels and can carry many fixed networks, such as Ethernet, IP, ATM and UMTS. HIPERlan/2 defines two different CL layers, which are based on ATM cells and based on packets. The former is used to connect ATM networks, and the latter can be used in many packet-based network structures.

The packet-based CL has a general service part and a special service part, which can be used in different networks. At first, HiperLAN/2 defined a common part and defined the functions of specific services for Ethernet.

5 wireless network function

HiperLAN/2 standard defines metrics and signaling that support a large number of wireless network functions: dynamic frequency selection, link adaptation, wireless cellular handover, multi-beam antenna and power control.

5. 1 dynamic frequency selection HiperLAN/2 wireless network will automatically assign communication frequency to each AP. This is achieved through Dynamic Frequency Selection (DFS), which allows multiple operators to enjoy the available frequency bands while avoiding band interference. Each AP makes frequency selection based on the filtered coherent measurement of AP and its related MT.

5.2 Link adaptation

Link adaptive strategy is to solve the problem of wireless channel quality change. The signal-to-interference ratio varies with the location of system configuration and the traffic of surrounding wireless cells. Link adaptive strategy makes the robustness of physical layer change adaptively with the result of link quality measurement. Therefore, in each MAC frame, the mode of the physical layer is dynamically selected.

5.3 antenna

H/2 supports the use of multi-beam antennas to improve the link budget and increase the C/I ratio. The MAC protocol and H/2 frame structure allow up to 7 beams.

5.4 switching

The handover is initiated by mt. For example, MT makes necessary measurements on the surrounding AP and selects the appropriate AP for communication. There is no handover policy defined in the standard. For example, operators can choose to switch based on signal strength.

5.5 power control both MT and AP have transmitter power control. The power control of MT is mainly used to simplify the design of AP receiver. The power control of AP is partly for adjustment reasons, such as reducing the interference of satellite system.

6 concluding remarks

Hiperlan2 can connect with local area network and 3G cellular network at a speed of up to 54 Mbps, providing mobility and quality of service support for future multimedia applications. We believe that Hiperlan/2, Bluetooth technology, wireless local area network and the third generation cellular system provide a complete communication environment for future mobile computing devices.