1. Field of the Invention
The present invention relates to the relay of signals in a wireless network.
2. Description of the Related Art
In a wireless network, such as an ad hoc network, in which a signal is relayed from a source node to a destination node through a plurality of intermediate nodes, indiscriminately routed signals are apt to collide or interfere, causing transmission errors. Japanese Unexamined Patent Application Publication No. 2001-244983 therefore equips the intermediate nodes with directional beam antennas; by measuring the strength of signals received from various directions and keeping a table of signal strengths and directions, an intermediate node can select a neighboring node that will minimize both radio interference and the number of hops to the destination, and beam its signal to the selected node. Beaming signals in this way prevents transmission errors due to interference, and reduces power consumption as well. The same directional beam antenna is used for both transmitting and receiving, the beam direction being changed by, for example, electronic control of scanning intervals across a phased array of antenna elements.
A drawback of this arrangement is that the antenna cannot be used for transmitting and receiving simultaneously. Each continuously received signal packet must therefore be stored in a buffer memory. After the entire packet has been received, the antenna beam direction is switched, the stored signal is read from the buffer, and transmission begins. The relay process accordingly includes a delay at least equal to the length of the packet. Switching the antenna direction, converting the received signal to a form storable in the buffer, and switching the buffer between read and write access also adds slightly to the delay.
The delay accumulates from one relay node to the next. Particularly in a network employing low-power signal transmission, since the number of hops on a route tends to be large, the cumulative delay may become substantial. If the transmitted signal is an audio or video signal, the delay may seriously impair the quality of the received sound or picture.
An object of the present invention is to reduce the transmission delay of signals transmitted in a wireless communication network.
The signal relaying apparatus according to the present invention includes a plurality of devices for relaying signals to and from distant nodes in the network. At least one of the devices is an antenna device, but the devices may include one or more cable devices as well. The apparatus also includes a receiver that receives a signal through one of the devices and a transmitter that transmits the same signal through another of the devices, and may include an additional intermediate unit for amplifying or temporarily storing the received signal before it is transmitted. The apparatus may further include a switch for connecting the receiver to an arbitrary one of the devices while connecting the transmitter to another arbitrary one of the devices.
If the devices are antennas, then by using two antennas simultaneously, the invented apparatus avoids the need to store an entire continuously received packet in a signal buffer before beginning transmission of the packet on the next hop. Even if a signal buffer is employed, transmission of the packet through one antenna can begin while the packet is still being received through another antenna. Delays are thereby shortened, and high transmission quality can be maintained, even for audio and video signals. Similar advantages are obtained when one or more of the devices are cables.
In the attached drawings:
Embodiments of the invention will now be described with reference to the attached drawings, in which similar elements are indicated by analogous reference characters (e.g., three-digit numbers differing only in the first digit).
Referring to
As shown in
The signal relaying apparatus 100 can operate in two different relay modes: a signal amplifying mode and a signal buffering mode. In the signal buffering relay mode, the radio-frequency signal received by one antenna sector is demodulated and temporarily stored in the signal buffer 109, then modulated onto a carrier signal and transmitted from a different antenna sector. In the signal amplifying relay mode, the received radio-frequency signal is amplified and transmitted from the other antenna sector immediately, without being demodulated or stored in the signal buffer. Which mode to use is determined by the route control unit 111 from, for example, priority information included in the received signal, or in control signals transmitted and received among different base stations.
The signal amplifying relay mode operates as follows. On command from the route control unit 111, the media access control unit 110 has the switch controller 107 connect the receiver 104 to, for example, sector 3 of the sector antenna 120 and the transmitter 106 to, for example, sector 1. The amplifier 105 receives the radio-frequency signal received from sector 3 through the receiver 104, amplifies it, and sends it to the transmitter 106. The transmitter 106 transmits the amplified received signal from sector 1 on the next hop toward its ultimate destination. The frequency at which sector 1 receives the signal and the frequency at which sector 3 transmits the signal may be the same or may differ. For example, the frequency may be down-converted in the receiver 104, then up-converted to a different frequency in the transmitter 106. In either case, because the received signal is not stored in the signal buffer 109, the delay from receiving to transmitting is very small, being equal only to the signal propagation delay in the electrical circuit elements of the signal relaying apparatus.
The signal buffering relay mode operates as follows. On command from the route control unit 111, the media access control unit 110 has the switch controller 107 connect the receiver 104 to, for example, sector 3 of the sector antenna 120 and the transmitter 106 to, for example, sector 1. The radio-frequency signal received by sector 3 is demodulated by the receiver 104, and the demodulated signal is sent to the signal buffer 109 and stored. The signal stored in the signal buffer 109 is read out at a fixed transmission timing and sent to the transmitter 106. The transmitter 106 modulates the signal onto a carrier signal and transmits it from sector 1 on the next hop toward the destination. The delay from receiving to transmitting is longer in this mode than in the signal amplifying relay mode, but the delay is shorter than in the conventional apparatus described above, because transmission of a continuously received signal packet through one antenna sector can begin while the packet is still being received through another antenna sector.
Next, an example of signal propagation through a mobile wireless communication network having a plurality of relay nodes will be described with reference to
Referring to
In time slot 5, base station A uses antenna sector 1 for transmitting on link 1A and antenna sector 2 for receiving on link AB, base station B uses antenna sector 3 for transmitting on link AB and antenna sector 2 for receiving on link BC_1, and base station C uses antenna sector 1 for transmitting on link BC_1 and antenna sector 2 for receiving on link 2C, establishing a communication path from mobile terminal 2 through base stations C, B, and A, in that order, to mobile terminal 1.
The above operations are repeated in time slots 9 and 13. It is accordingly possible to carry out bi-directional communication between mobile terminals 1 and 2 without delay due to buffering (delay due to storage of the signal in a signal buffer) by using time slots 1, 5, 9, 13, and so on. Voice or video communication service can be provided between these mobile terminals in this way.
In like manner, base stations B and D relay communication between mobile terminals 3 and 4 in time slots 2, 6, 10, . . . ; base station B relays communication between mobile terminal 5 and base station C in time slot 3, 7, 11, . . . ; and mobile terminal 6 communicates directly with base station C in time slots 4, 8, 12, . . . . These time slots can be used to provide voice or video communication service between mobile terminals 3 and 4, between mobile terminal 5 and a stationary terminal (not shown) connected to base station C, and between mobile terminal 6 and another stationary terminal (not shown) connected to base station C. The time slots are assigned in a way that avoids signal interference and packet collisions.
Referring to
As shown in
As in the first embodiment, the signal relaying apparatus 200 can operate in a signal amplifying relay mode and a signal buffering relay mode.
In the second embodiment, the signal amplifying relay mode operates as follows. At the command of the route control unit 211, the media access control unit 210 has the switch controller 207 connect the receiver 204 to, for example, the antenna sector 5 and the transmitter 206 to the cable 231. The amplifier 205 receives a signal received by the antenna sector 5 through the receiver 204, amplifies it, and sends it to the transmitter 206. The transmitter 206 transmits the amplified signal through the cable 231 to the antenna sector 4 at the other signal relaying apparatus. The other signal relaying apparatus then transmits the signal from the antenna sector 4 on the next hop toward the destination.
In this mode, the signal is received by the antenna (or cable) and transmitted through the cable (or antenna) without having to be stored in and read from the signal buffer 209. The delay from receiving to transmitting is therefore very small, being equal only to the signal propagation delay in the electrical and optical circuit elements of the signal relaying apparatus.
The signal buffering relay mode operates as follows. On command from the route control unit 211, the media access control unit 210 has the switch controller 207 connect the receiver 204 to, for example, the antenna sector 5 and the transmitter 206 to the cable 231. In this case, the radio-frequency signal received by antenna sector 5 is demodulated by the receiver 204, and the demodulated signal is sent to the signal buffer 209 and stored. The signal stored in the signal buffer 209 is read out at a fixed transmission timing and sent to the transmitter 206. The transmitter 206 modulates the signal onto a radio-frequency carrier signal and transmits it to the other signal relaying apparatus through the cable 231.
Next, an example signal propagation through a mobile wireless communication network having a plurality of relay nodes with the signal relaying apparatus of the first embodiment and a plurality of base stations with the signal relaying apparatus of the second embodiment will be described with reference to
Each base station operates in time slots having a fixed duration as shown in
When mobile terminal 7 communicates with mobile terminal 8, the communication path may consist of, for example, link 7E (a wireless link between mobile terminal 7 and base station E_5), link E_5E_4 (the cable link between base stations E_5 and E_4), link EC (a wireless link between base stations E_4 and C), and link 8C (a wireless link between base station C and mobile terminal 8).
As can be seen from
Like the first embodiment, the second embodiment can provide voice or video communication service between even distant mobile terminals without the accumulation of long delays at relay nodes en route. In addition, by connecting one or more pairs of mutually separated base stations with optical fiber cables, the second embodiment can reduce the number of wireless relay hops, thereby reducing interference and simplifying the routing of signals.
Referring to
As shown in
The signal amplifying relay mode in the third embodiment operates, for example, as follows. At the command of the route control unit 311, the media access control unit 310 has the switch controller 307 connect the receiver 304 to sector 3 and the transmitter 306 to cable 331. The amplifier 305 receives a radio-frequency signal received by sector 3 through the receiver 304, amplifies it, and sends it to the transmitter 306. The transmitter 306 transmits the amplified radio-frequency signal through cable 331 to the other signal relaying apparatus. Needless to say, the switch may controller may connect the receiver 304 to cable 332 instead of an antenna sector, and may connect the transmitter 306 to an antenna sector instead of cable 331.
In this mode, the signal is received by an antenna (or a cable) and transmitted through a cable (or an antenna) without having to be stored in and read from the signal buffer. The delay from receiving to transmitting is therefore very small, being equal only to the signal propagation delay in the electrical and optical circuit elements of the signal relaying apparatus.
The signal buffering relay mode operates as follows. On command from the route control unit 311, the media access control unit 310 has the switch controller 307 connect the receiver 304 to, for example, sector 3 and the transmitter 306 to, for example, cable 331. The radio-frequency signal received by sector 3 is demodulated by the receiver 304, and the demodulated signal is sent to the signal buffer 309 and stored. The signal stored in the signal buffer 309 is read out at a fixed transmission timing and sent to the transmitter 306. The transmitter 306 modulates the signal onto a radio-frequency carrier signal and transmits it to the other signal relaying apparatus through cable 331.
Next, an example of signal propagation through a wireless communication network having a plurality of relay nodes with the signal relaying apparatus of the first embodiment and a plurality of relay nodes with the signal relaying apparatus of the third embodiment will be described with reference to
When mobile terminal 1 communicates with mobile terminal 2, the communication path may consist of, for example, link 1A (a wireless link between mobile terminal 1 and base station A), links AB_1 and AB_2 (cable links between base station A and base station B), link BC_1 (a wireless link between base stations B and C), and link 2C (a wireless link between base station C and mobile terminal 2).
This communication path is implemented in time slots 1, 5, 9 and 13 in
Like the preceding embodiments, the third embodiment enables bi-directional communication between even distant mobile terminals 1 and 2 to take place without long cumulative delays due to buffering en route. In addition, the third embodiment allows base stations to be interconnected by cable links that are selected and used in substantially the same way as the wireless links; accordingly, when wireless communication resources become inadequate, further communication resources can be added with cables, without increasing the number of relay nodes.
The present invention is suitable for short-haul networks such as local area networks (LANs) in which the wireless propagation delay is negligible and time slot alignment poses no particularly problems, but the invention may also be practiced in long-haul networks if the base stations exchange information about the wireless propagation delay and adjust their transmission timing so that the signals arriving in different time slots at a given node are properly separated on the time axis.
In the embodiments described above, the signal relaying apparatus has a structure that enables it to operate in both signal amplifying and signal buffering relay modes, but it may also have a structure in which it can operate in just one of these two modes.
Those skilled in the art will recognize that further variations are possible within the scope of the invention, which is defined in the appended claims.
Number | Date | Country | Kind |
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2003-406993 | Dec 2003 | JP | national |
Number | Name | Date | Kind |
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6132306 | Trompower | Oct 2000 | A |
6690657 | Lau et al. | Feb 2004 | B1 |
Number | Date | Country |
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3-212032 | Sep 1991 | JP |
2000-101454 | Apr 2000 | JP |
2001-244983 | Sep 2001 | JP |
2001-345754 | Dec 2001 | JP |
2002-152098 | May 2002 | JP |
2003-115842 | Apr 2003 | JP |
2003-406993 | Nov 2007 | JP |
Number | Date | Country | |
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20050122931 A1 | Jun 2005 | US |