Brief Introduction to standard Wireless Access Network Technology HiperLAN/2

China's wireless access network is still developing very rapidly, and the standard technology HiperLAN/2 also makes it more standardized. Here we mainly introduce the network structure and functions, this section describes how standard technology HiperLAN/2 works. Because it is not restricted by physical lines, wireless access networks have incomparable advantages over wired networks. Various vendors have launched a series of 802.11-standard wireless LANWLAN-based products to address the needs of Wireless Access Network LAN applications. These products provide bandwidth from 1 Mbps to 11 Mbps. However, the performance of these wireless access network products is far from comparable to that of traditional fixed network products, this makes the performance of today's wireless access networks and wide-area cellular networks using GSM, AMPS and other technologies seem to have no substantial difference. Although it also supports some low-speed (about 10 Kbps) data communication, the main applications of these wireless access networks still support voice services. To meet future Internet/Intranet access needs, the industry is developing a new generation of WLAN and cellular network technologies, which will be used in QoS to create multi-service networks), security and performance improvements.

Network Structure and Functions

Displays the topology of A HiperLAN/2 network. Mobile Terminal MT) communicates with Access Point AP through a wireless interface determined by HiperLAN/2 standard. MT users can freely move in the HiperLAN/2 network, and HiperLAN/2 can ensure optimal Transmission Performance for users and MT users. One MT only communicates with one AP at a time. No matter where the user moves, HiperLAN/2 wireless networks can detect the AP that can provide the best performance for the MT at every time, and automatically establish contact with the AP. It is reported that two MT devices can communicate directly without using wireless interfaces. However, this technology is still in the R & D stage and details are not yet made public. HiperLAN/2 defines detection and conversion signaling to support many wireless network features, including dynamic frequency selection DFS) function, Link adaptive, wireless cell conversion, multi-bundle antenna, and power control.

Dynamic Frequency Selection

This feature allows several network providers to share available spectrum and can be used to avoid mutual interference between frequencies. Each AP selects the frequency by filtering interference Metering by the AP and its associated MT.

Working Principle

In HiperLAN/2, each AP uses the DFS algorithm to select an appropriate frequency. First, MT detects the signal strength and selects the most appropriate AP to establish a connection with it. MT receives a mac id from the selected AP), then switches the link function and determines the authentication process and encryption algorithm to be used, and which aggregation layer is used for user communication. After key exchange and authentication, the MT can establish a connection with the AP. Finally, establish a user connection in the Data Link Control Layer (DLC), and then the user can communicate. MT will send and receive data through two established connections by default in HiperLAN. These two connections support two different Q-tag ing priority queues. Of course, you can also support more priority queues ). The Ethernet aggregation layer ensures that the priority of each Ethernet frame is mapped to an appropriate data link layer user connection based on the predefined ing scheme.

MT can decide to join one or more multicast groups. The HiperLAN/2 network can be configured to use N single-channel broadcasts to achieve the optimal transmission quality. You can also assign a separate MAC Number MACID to each group) to reserve bandwidth for it. If a separate MAC number is assigned to a multicast group, the ing scheme is IP address-IEEE address-MAC Number. When MT moves, if it detects that an AP is more suitable for communication, such as better signal strength), it performs a conversion. All established connections will use APAP signaling and be automatically converted to the new AP through a fixed LAN. When MT is more accurate to the user) wants to disconnect from the LAN, MT disconnects the request so that all connections between the MT and AP are disconnected. When the MT moves beyond the coverage of HiperLAN/2, all connections between the MT and AP are also disconnected.

Main features

HiperLAN/2 has a high transmission rate. Its physical layer transmission rate can reach up to 54 Mbps, and the third layer transmission rate can reach up to 25 Mbps. To achieve this high rate, HiperLAN/2 uses a modulation method called Orthogonal Frequency Digital Multiplexing OrthogonalFrequencyDigitalMultiplexing, OFDM) to transmit analog signals. OFDM is very effective in time-dispersed environments such as offices. The signals sent from wireless access networks in these regions may be reflected by many points, so that they will produce different propagation times before they finally reach the receiver. On the physical layer, HiperLAN/2 uses the brand new media control layer MAC protocol. It uses a Dynamic Time Division Duplex technology to make the most effective use of wireless access network resources.

Connection-oriented

Traditional wireless networks are not connected. In the HiperLAN/2 network, you must first use the signaling function of the HiperLAN/2 Control Panel to establish a connection between the MT and the AP before data transmission. The connection is established using the radio interface time division multiplexing technology. There are two types of connections used in HiperLAN/2: point-to-point connections and single-point-to-point connections. Point-to-point connections are bidirectional, while single-point-to-point connections are unidirectional, that is, they only point to the mobile terminal MT. In addition, a dedicated broadcast channel is used to transmit data from an AP to all terminals (MT.

QoS support

The connection-oriented Feature of HiperLAN/2 makes it easy to meet QoS requirements. You can assign a specified QoS for each connection, determine the bandwidth, latency, congestion, bit error rate, and other requirements of the connection. In HiperLAN/2, it is also possible to use a simpler method, that is, each connection can be assigned a different priority mark. Together with the high transmission rate, this QoS ensures that different data sequences, such as videos, voice and data, can be transmitted at high speed at the same time.

Automatic Frequency allocation

In the HiperLAN/2 network, you do not need to manually plan the frequency as in the cellular network (such as GSM. A wireless base station is called an access point AP in HiperLAN/2. It supports selecting the most appropriate wireless channel for the transmission of each AP within the coverage range. (Connected to version D26) each AP monitors neighboring AP and other wireless resources in the HiperLAN/2 environment, and select the most suitable transmission channel based on the two principles that the wireless channel has been occupied by other APs and that the interference to the wireless network environment is minimized.

Security Support

HiperLAN/2 supports authentication and encryption. By using the authentication mechanism, the AP and MT can authenticate each other to ensure that authorized access to the network is from the AP perspective ), or make sure that the access to valid network providers is from the MT perspective ). The authentication mechanism in HiperLAN/2 depends on some other support functions, such as Directory Service), but these support functions are not included in HiperLAN/2 technology. Users can use encryption technology to prevent real-time eavesdropping and man-in-the-middle attacks when communicating on established connections.

Mobility Support

MT will be able to automatically transmit and receive data from the nearest AP. More specifically, the AP used by MT provides the optimal signal-to-noise ratio for the wireless access network. Therefore, when the user and MT move, MT may detect another AP with better wireless access network transmission performance than the AP currently in use. At this time, MT is automatically converted to this AP. All established connections will be transferred to the new AP, so that the MT is still on the HiperLAN/2 network, so communication will not be interrupted. However, packet loss may occur during the conversion. If a MT exceeds the coverage of standard technology HiperLAN/2 for wireless access networks in a certain period of time, the MT may be disconnected from the HiperLAN/2 network, this will release all original connections.

Independent networks and applications

The HiperLAN/2 protocol stack has a flexible structure, so it is easy to adapt and integrate with a variety of fixed networks. For example, a HiperLAN/2 network can be used for the last segment of a switched Ethernet, but it may also be used for other configurations, such as an access network for a third-generation cellular network. All applications that can run on a fixed network can run on the HiperLAN/2 network.

Low Power Consumption

In HiperLAN/2, the mechanism of saving power consumption by MT is based on the dormant state started by MT. MT can request the AP to enter a low-power sleep state at any time and determine the time of this state. When the negotiated sleep period expires, MT searches for whether the AP sends a wake-up instruction. If no wake-up indicator is found, MT will be converted to the low-power status and enter the next sleep period. During sleep, the AP delays all waiting data transmission tasks until the corresponding sleep period ends in MT. HiperLAN/2 supports different sleep times to meet different requirements for short latency or low power.