An Access Method for a Multi-Hop Wireless Network

Technical Field

This invention relates to an access method for a multi-hop wireless network, and more particularly, to an access method for a multi-hop wireless network in a beyond third genera- tion/fourth generation (B3G/4G) mobile communication system.

Background Art

As the third generation (3G) mobile communication is starting its commercial application, it has come to the pre-develop- ment stage for B3G/4G technology of higher speed, higher fre ^¬ quency spectrum efficiency, better coverage and more powerful business supporting capabilities; it has been planned to com ^¬ plete the frequency allocation by 2007, to accomplish major criteria by 2010, to start commercial application by 2012 and to put into large-scale commercial application by 2015. The demand for frequency spectrum by B3G systems should be at least 600 MHz. As currently available frequency bands do not meet this demand, higher frequency bands will be allocated to B3G and 4G systems.

Although relatively high frequency bands can solve the fre ^¬ quency allocation problem for B3G systems, the higher the frequency band, however, the poorer the electromagnetic wave's mobility or penetrating capabilities will be. In this case, the electromagnetic waves would get closer and closer to straight line propagation, and if there were buildings, there would be many "shadowy" areas in a cell, beyond the reach of the electromagnetic waves. For example, if a mobile node (MN) is behind a building, due to the signals' poor ca ^¬ pability to get around, signals would not be able to reach the mobile node by going around the building, furthermore, due to the signals' poor penetrating capability, the signals

would not be able to reach the mobile node by going through the building, therefore this mobile node may not be able to receive signals coming from a base station.

Furthermore, the higher the frequency band, the higher the attenuation of the electromagnetic waves will be, and hence the transmitting power will attenuate. The transmitting power attenuation of a base station would lead to a reduced coverage range in a cell, or if the coverage range is not changed, it would lead to less ideal power control at the cell's edge, which would cause many transmitting errors. Also, because people wish to reduce the influence of electro ^¬ magnetic radiation on the human body, a base station' s trans ^¬ mitting power would have to be reduced, which would further aggravate the problem of less ideal power control at the cell's edge.

One solution to the above problem is to re-divide the honey ^¬ comb cells so that the original cells can be reduced to the range that can be covered by the base station power, and then to set up one base station in each size-reduced cell. How ^¬ ever, this method requires connecting each base station by optical fibers, which is very inconvenient in practice. When the optical fibers have to pass through areas which are pri- vate or through other areas impractical for laying optical fibers, the inconvenience is greater still.

For this reason, there exists in the field of wireless commu ^¬ nication the concept of a multi-hop network, in which a relay node (RN) is added between a base station and a mobile node so as to form a route of base station - relay node - mobile node. There may be only one of the above mentioned relay nodes but there can also be many of them. With such a multi- hop network the power needed by each relay node is signifi- cantly reduced, since one node in a multi-hop network only needs enough transmitting power to reach an adjacent node. Secondly, due to the very low power at each node in a mesh network, the equipment at different parts of a network can

actually transmit simultaneously at the same frequency with ^¬ out causing any interference. Such duplicated use of fre ^¬ quency increases the network' s space capacity, and the short distances between nodes lead to an increased network band- width.

Fig. 1 is an illustrative signalling flowchart for a mobile node to be connected for the first time into a multi-hop net ^¬ work in the prior art. The mobile node MN in the figure first transmits an access request message to the nearest re ^¬ lay node RN, which relay node relays said access request mes ^¬ sage to the next relay node, until said access request mes ^¬ sage is relayed to an access point (AP) ; the access point AP is connected to a service agent (SA) , which service agent SA contains route and access information. If the service agent SA authenticates the information from the mobile node as le ^¬ gal, it would inform the access point AP, and AP would then establish a route for returning a message to the mobile node. Then the AP transmits an access authorization message to a relay node by the selected route, and the relay node relays this access authorization message to the next relay node un ^¬ til this access authorization message is relayed to said mo ^¬ bile node.

Fig. 2 is an illustrative signalling flowchart for the mobile node, after having moved, to be connected into the multi-hop network in the prior art. The dashed line mobile node MN in the figure represents its position before the movement, the mobile node MN first moves in the direction shown by the ar- row, then the mobile node MN transmits an access request mes ^¬ sage to the nearest relay node RN, which relay node relays said access request message to the next relay node, until said access request message is relayed to the access point AP; the access point AP is connected to the service agent SA, which service agent SA contains route and access information. If the service agent SA authenticates the information from the mobile node as legal, it would inform the access point AP, and AP would then change the route for returning a mes-

sage to the mobile node. Then the AP transmits an access au ^¬ thorization message to a relay node by the changed route, which relay node relays this access authorization message to the next relay node until this access authorization message is relayed to said moved mobile node.

However, because there are many nodes, when a mobile node is accessing a multi-hop network, the processing of encoding, decoding and routing information has to be performed via a network layer, an access layer and a physical layer at every one of the access point AP, relay nodes RN and the mobile node MN. The network accessing time and the access delay would therefore be quite long, which would be disadvantageous to a mobile node's seamless access during its movement.

Contents of the Invention

An object of this invention is to provide an access method for a multi-hop wireless network, so that when a mobile node moves from one cell into another cell, the access speed can be improved by using this method to ensure that the communi ^¬ cation data, especially the voice data, are not interrupted.

To achieve the above object, the technical solution of this invention is realized as follows: an access method for a multi-hop wireless network, to be used in a distributed multi-hop wireless network, which network comprising an access point, a service agent connected to said access point, at least one relay node and at least one mobile node, charac- terized in that said method comprises the following steps of: (1) informing, by each mobile node at the time of its regis ^¬ tration in said wireless network, to at least one relay node adjacent to said mobile node of the access information rele ^¬ vant to said mobile node; (2) storing the access information relevant to said mobile node in said at least one relay node adjacent to said mobile node;

(3) informing, by said at least one relay node, all the other relay nodes adjacent to said mobile node of said access information relevant to said mobile node, or informing, by said relay node, at least one relay node predicting the move- ment of said mobile node of said access information relevant to said mobile node ;

(4) transmitting by said mobile node an access request mes ^¬ sage to a relay node adjacent to said mobile node;

(5) returning to said mobile node an access authorization message by said relay node having received the access request message;

(6) transmitting a route update message by said relay node to the next relay node, and relaying said route update mes ^¬ sage in turn by said next relay node to other relay nodes un- til said route update message is relayed to said access point;

(7) performing route update by said access point or said service agent.

The technical solution by this invention can also be realized as follows: an access method for a multi-hop wireless network, to be used in a centralized multi-hop wireless network, said network comprising an access point, a service agent connected to said access point, at least one relay node and at least one mobile node, characterized in that said method comprises the following steps of:

(1) informing, by each mobile node at the time of its regis ^¬ tration in said wireless network, said access point of the access information relevant to said mobile node; (2) storing the access information relevant to said mobile node in said access point or said service agent; (3) informing, by said access point, all the relay nodes adjacent to said mobile node of said access information rele ^¬ vant to said mobile node, or informing, by said access point, at least one relay node predicting the movement of said mo ^¬ bile node of said access information relevant to said mobile node ;

(4) transmitting by said mobile node an access request mes ^¬ sage to a relay node adjacent to said mobile node;

(5) returning to said mobile node an access authorization message by said relay node having received the access request message;

(6) transmitting a route update message by said relay node to the next relay node, and relaying said route update mes ^¬ sage in turn by said next relay node to other relay nodes un ^¬ til said route update message is relayed to said access point;

(7) performing route update by said access point or said service agent.

Wherein, after said relay node has stored the access informa- tion relevant to said mobile node, it deletes the received access information; or after having received a delete signal issued by a relay node in current contact with said mobile node, said relay node deletes the received access informa ^¬ tion. After said relay node has stored the access information relevant to said mobile node, the time to delete the received access information is set by said relay node or said access point .

In addition, the manner of said informing is by way of broad- cast, multicast or unicast.

It can be seen that the method provided by this invention has the following advantages:

(1) The access method for a multi-hop wireless network pro ^¬ vided by this invention has moved the access information originally located in the network' s service agent to a re ^¬ lay node adjacent to a mobile node, so that when the mo ^¬ bile node is being connected, it no longer needs to ac- quire the access authorization message from the access point, but only to acquire the access authorization mes ^¬ sage from an adjacent relay node, which has greatly re-

duced the transmission of the access signal and greatly reduced the mobile node's access time.

(2) The access method for a multi-hop wireless network pro ^¬ vided by this invention enables seamless access by a mo- bile node during high speed movement or operating from one cell to another cell, which is very important for data transmission, especially voice data transmission, in a B3G network, so that a user does not experience the phenomenon of temporary interruption during a conversation, and the voice quality can be kept clear all the time.

(3) The access method for a multi-hop wireless network pro ^¬ vided by this invention only needs to set a storage area at a relay node in the network for storing the access in ^¬ formation corresponding to each mobile node, so the changes made to the current technical equipment are small and they save costs.

(4) The access method for a multi-hop wireless network pro ^¬ vided by this invention would not affect the application of the existing technology, so if the latest access infor- mation cannot be obtained by using this method, access can still be made by following the method of the existing technology, therefore it is compatible with the existing technology.

Description of the Drawings

Fig. 1 is an illustrative signalling flowchart for a mobile node to be connected for the first time into a multi-hop net ^¬ work in the prior art. In this figure, MN is a mobile node, RN is a relay node and AP is an access point.

Fig. 2 is an illustrative signalling flowchart for the mobile node, after having moved, to be connected into a multi-hop network in the prior art. Fig. 3 is an illustrative signalling flowchart for a mobile node, after having moved, to be connected into a multi-hop network, which is a distributed multi-hop wireless network, in a first embodiment of this invention.

herein belowFig. 4 is an illustrative signaling flowchart for a mobile node, after having moved, to be connected into a multi-hop network, which is a centralized multi-hop wireless network, in a second embodiment of this invention.

Practical Embodiments

A prerequisite of the present invention is that a multi-hop network is used in B3G and 4G wireless mobile communication networks, wherein a base station is usually referred to as an access point AP, and a relay node RN is added between the ac ^¬ cess point and mobile node. There may be only one of the above relay nodes RN, or there can be many. At the network's access point AP, there is a service agent SA, which service agent stores the route information for the mobile node MN.

Said service agent SA can also be located at any other posi ^¬ tion in the network connected to the access point.

Fig. 3 is an illustrative signaling flowchart for a mobile node, after having moved, to be connected into a multi-hop network, which is a distributed multi-hop wireless network, in a first embodiment of this invention.

In Fig. 3, MN is a mobile node, such as a mobile station or a notebook computer with a wireless network card. The dashed line in Fig. 3 is the mobile node's initial position.

The mobile node is turned on to register in the network, and at the same time at least one relay node adjacent to said mo- bile node, such as the relay node RNl above the dashed line, is informed of the access information relevant to this mobile node; the relay node retains a copy of the access information relevant to this mobile node, i.e. the access information re ^¬ lating to this MN is stored in RNl, and at the same time AP is informed of the registration information relevant to this mobile node.

Relay nodes adjacent to RNl, such as RN2 and RN3 are monitor ^¬ ing and predicting MN' s movement; if one or several adjacent relay nodes have predicted MN' s movement in their vicinity, RNl would inform the one or several relay nodes of this MN' s access information; or if the adjacent relay nodes are not required to predict MN' s movement, RNl can inform all the ad ^¬ jacent relay nodes RN2 and RN3 of this MN ' s access informa ^¬ tion. The manner of informing can be by way of broadcast, or it can also be by multicast or unicast.

The mobile node MN moves from its initial position, after which movement the relay node most adjacent to MN is RN2. Since RN2 has monitored MN' s movement, RNl informs RN2 of MN' s access information, or RNl informs adjacent relay nodes (including RN2) of MN' s access information.

The mobile node MN transmits to the closest relay node RN2 an access request message, since RN2 has already stored the ac ^¬ cess information for this mobile node MN, RN2 can immediately return an access authorization message to this mobile node MN.

The relay node RN2 transmits a route update message to the next relay node RN3, and RN3 relays this route update message to the access point AP.

The above access point AP performs route updating, and stores the updated route information in the service agent SA con ^¬ nected with said AP.

After having stored the access information relating to this mobile node in the relay node RNl for some time, the received access information is deleted, and this time period can be set by the relay node; or after receiving a delete signal is- sued by the relay node RN2 which has current contact with said mobile node, the relay node RNl deletes the stored ac ^¬ cess information relating to this MN.

Assuming that after the mobile node MN' s movement the relay node RN2 closest to MN does not have this MN' s latest access information, this MN would transmit an access request message to its other adjacent relay nodes. If the other relay nodes adjacent to this MN do not have this MN' s latest access in ^¬ formation either, MN would transmit the access request mes ^¬ sage to RN2, and RN2 would then relay this access request message to other adjacent relay nodes, until this access re ^¬ quest message is sent to the access point AP, hence following the flowchart of the prior art shown in Fig. 1 to accomplish the access.

Fig. 4 is an illustrative signaling flowchart for a mobile node, after having moved, to be connected into a multi-hop network, which is a centralized multi-hop wireless network, in a second embodiment of this invention.

In Fig. 4, MN is a mobile node, such as a mobile station or a notebook computer with a wireless network card. The dashed line in Fig. 4 is the mobile node's initial position.

The mobile node is turned on to register in the network, at the same time the access point AP is informed of the access information relevant to this mobile node; and AP sends a no- tice to relay nodes adjacent to the mobile node MN, such as RNl and RN2, to inform them of the access information relating to this MN. Then RNl and RN2 store the access informa ^¬ tion relating to this MN separately.

One or several relay nodes adjacent to RNl, such as RN2 and RN3 are monitoring and predicting MN' s movement; assuming that RN2 has predicted MN' s movement in its vicinity, the ac ^¬ cess point AP would inform RN2 of this MN' s access informa ^¬ tion; or if the adjacent relay nodes are not required to pre- diet MN' s movement, the access point AP can inform the relay nodes RNl and RN2 adjacent to this MN directly of the MN's access information. The manner of informing can be by way of broadcast, or it can also be by multicast or unicast.

The mobile node MN moves from its initial position, after which movement the relay node most adjacent to MN is RN2. Since the access point AP has informed RN2 of MN' s access in- formation, RN2 has already stored this MN' s access informa ^¬ tion.

The mobile node MN transmits to the closest relay node RN2 an access request message, since RN2 has already stored the ac- cess information of this MN; RN2 can immediately return an access authorization message to this MN.

The relay node RN2 transmits a route update message to the next relay node RN3, and RN3 in turn relays this route update message to the access point AP.

The above access point AP performs route updating, and stores the updated route information in the service agent SA con ^¬ nected with said AP.

After having stored the access information relating to this mobile node in the relay node RNl for some time, the received access information is deleted, and this time period can be set by the relay node; or after receiving a deletion signal issued by the relay node RN2 which has current contact with said mobile node, the relay node RNl deletes the stored ac ^¬ cess information relating to this MN.

Assuming that after the mobile node MN' s movement, the relay node RN2 closest to MN does not have this MN' s latest access information; this MN would transmit an access request message to its other adjacent relay nodes. If the other relay nodes adjacent to this MN do not have this MN' s latest access in ^¬ formation either, MN would transmit the access request mes- sage to RN2, and RN2 would then relay this access request message to other adjacent relay nodes, until this access re ^¬ quest message is sent to the access point AP, hence following

the flowchart of the prior art shown in Fig. 1 to accomplish the access.

It can be seen from the above two embodiments that, by the access methods of this invention, the access information originally located in the network' s service agent is moved into a relay node adjacent to the mobile node, so that at the time of the mobile node's access there is no need to acquire the access authorization message via the access point, and it only needs to acquire the access authorization message from an adjacent relay node, so the access time for the mobile node is greatly reduced, and seamless access during the mo ^¬ bile node's movement is ensured.