Synchronization of terminals in a radio link system

• US 6,954,439 B2
• Filed: 03/26/2001
• Issued: 10/11/2005
• Est. Priority Date: 10/23/1998
• Status: Expired due to Term

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Nokia Corporation
• Inventors: Kuru, Lauri, Makinen, Jarmo, Pulkkinen, Otto
• Primary Examiner(s): NGUYEN, STEVEN H D
• Application Number:
  US09/817,886
• Publication Number:
  US 20010014083A1
• Time in Patent Office: 1,660 Days
• Field of Search: 370/280, 370/350, 370/347, 370/294, 370/503, 370/507, 370/508, 455/561
• US Class Current: 370/280
• CPC Class Codes: H04B 7/2678 Time synchronisation
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 92/10 between terminal device and access point, i.e. wireless air interface

Abstract

The objective of the invention is to increase the potential hop density of single frequency TDD radio links by allowing a set of closely located terminals to use a single channel. This is possible when transmission and reception periods of the terminals are synchronized so that the transmit period of any of the terminals in a terminal group does not overlap with the receive period of any of the terminals in the group. Synchronization is achieved by selecting at least one terminal in a hub site as a super master terminal. This terminal gives timing through a common bus to the rest of the terminals in the group. These terminals use the received timing for adjusting their own timing i.e. for adjusting the starting moment and ending moment of the transmission and reception periods in such a manner that none of terminals is sending a burst while another terminal is receiving.

Claims

1. A method of synchronizing transmission and reception periods of a group of terminals in a fixed radio link system operating in time division duplex mode and in which the group of terminals is located in a hub site, comprising the steps of:

arranging a common bus;

choosing one terminal from the group as a super master terminal which sends a synchronization signal to the common bus;

choosing the rest of the terminals from the group as master terminals which receive the synchronization signal from the common bus;

timing transmission periods of every individual master terminal in accordance with the synchronization signal received from the common bus in such a manner that the transmission periods overlap neither with reception periods of the master terminals, nor with those of the super master terminal; and

adding on the synchronization signal information about a radio frequency used by the super master terminal.

2. The method according to claim 1, further comprising:

sending synchronization information from the master terminal to the a remote terminal at an opposite end of the radio link; and

timing transmission and reception periods of the remote terminal in accordance with received synchronization.

3. The method according to claim 1, further comprising the step of:

tuning radio frequency of the transceivers of the master terminals to frequency announced by the super master terminal via the common bus.

4. The method according to claim 1, in which the group of terminals includes all the terminals in the hub site.

5. The method according to claim 1, wherein upon addition of a new terminal in the group, further comprising:

engaging the new terminal with the common bus;

receiving the synchronization signal and information about radio frequency from the common bus; and

carrying out timing and frequency tuning in the new terminal according to the synchronization signal and information about the radio frequency.

6. A The method according to claim 1, wherein upon missing the synchronization signal the common bus, further comprising:

choosing automatically one of the master terminals as a new super master terminal.

7. A fixed radio link system operating in time division duplex mode comprising:

at least one hub site including a number of hub transceivers operating at a same radio frequency, the hub site further comprising a common bus to which the hub transceivers are connected, a super master transceiver which is selected from the hub transceivers and which sends a synchronization signal to the common bus, and master terminals which are the rest of the hub transceivers and which receive the synchronization signal from the common bus;

a number of directive and sectored aerials pointing in different directions, each aerial being connected to a respective transceiver; and

a plurality of remote stations each having at least one remote transceiver communicating with a predetermined hub transceiver through a radio link,

wherein every individual master terminal sets the timing of transmission periods in accordance with the synchronization signal received from the common bus in such a manner that the transmission periods overlap neither with reception periods of the other master terminals nor with those of the super master terminal, and

wherein the super master transceiver sends information about the radio frequency used by the super master transceiver to the common bus.

8. The fixed radio link system according to claim 7, wherein the master terminals send synchronization information to corresponding remote terminals at the opposite ends of the radio links.

9. The fixed radio link system according to claim 8, wherein the remote terminals correct their timings responsive to the received synchronization information.

10. The fixed radio link system according to claim 7, wherein upon addition of a new transceiver to the hub site the new transceiver is configured to:

engage itself to the common bus for receiving the synchronization signal therefrom; and

carry out timing in response to said synchronization signal.

11. The fixed radio link system according to claim 7, wherein in response to disappearance of the synchronization signal from the common bus one of the master transceivers automatically changes into the super master transceiver.

12. The fixed radio link system according to claim 7, wherein the master transceiver turns itself to the radio frequency only when interference caused by external sources is below a predetermined level.