Efficient cell selection

• US 20080031368A1
• Filed: 11/29/2005
• Published: 02/07/2008
• Est. Priority Date: 11/29/2005
• Status: Active Grant

• Current Assignee: Optis Wireless Technology, LLC (Brevet Capital)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Asplund, Henrik, Lindoff, Bengt, Almgren, Magnus, Wiberg, Niclas, Furuskar, Anders
• Granted Patent: US 8,396,141 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 17/336 Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]
• CPC Class Codes: H04B 17/382 for resource allocation, admission control or handover
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems
• CPC Class Codes: H04W 48/20 Selecting an access point

Abstract

Systems and methods of cell selection are based on measures of frequency selectivity, time selectivity, and/or antenna selectivity. For example, the delay spread and coherence bandwidth of a channel are two measures of frequency selectivity that can be taken into account in the cell selection process. In addition to or instead of either delay spread or coherence bandwidth, Doppler frequency shift or coherence time (which are two measures of time selectivity) and/or antenna correlation or mean signal strength per antenna (which are two measures of antenna selectivity), among other parameters, can be determined and taken into account.

Claims

1. An apparatus in a communication system that includes a plurality of cells, wherein the cells transmit respective signals that include respective pilots through respective channels to a terminal, the apparatus comprising:

a signal strength estimator configured to generate first estimates of at least one of signal strengths and signal-to-interference ratios of signals received from respective cells;

an estimator configured to generate second estimates of at least one of a frequency selectivity, a time selectivity, and an antenna selectivity of respective channels between the terminal and respective cells; and

a cell selector configured to generate a cell selection based on the first estimates and the second estimates.

2. The apparatus of claim 1, wherein second estimates of the frequency selectivity of a channel include estimates of at least one of a coherence bandwidth and a delay spread of the channel.

3. The apparatus of claim 2, wherein the signals are orthogonal frequency division multiplex signals and the estimator is configured to generate second estimates by calculating a correlation in signal strength between pilots at different frequencies and at a same time instant.

4. The apparatus of claim 1, wherein second estimates of the time selectivity of a channel include estimates of at least one of a Doppler frequency shift and a coherence time of the channel.

5. The apparatus of claim 4, wherein the signals are orthogonal frequency division multiplex signals and the estimator is configured to determine correlations in signal strength between pilots at different time instants and at a same frequency for respective cells.

6. The apparatus of claim 1, wherein second estimates of the antenna selectivity of a channel include estimates of an antenna correlation of the channel.

7. The apparatus of claim 1, wherein the signals are orthogonal frequency division multiplex signals and the estimator is configured to determine correlations in signal strength between pilots from different antennas at a cell and at same time instants and same frequencies.

8. The apparatus of claim 1, wherein the signal strength estimator is configured to generate mean signal levels of pilots received from cells.

9. The apparatus of claim 8, wherein the signal strength estimator is configured to filter the mean signal levels generated.

10. The apparatus of claim 1, wherein the cell selector generates the cell selection by computing a cell selection function:

Cell=f(Sⁱ, T_dⁱ, F_Dⁱ, C_aⁱ)

for each cell, in which Cell represents a selected cell, Sⁱ represents a first estimate for a cell i, T_dⁱ represents a delay spread of the channel between the cell i and the terminal, F_Dⁱ represents a Doppler frequency shift of the channel between the cell i and the terminal, and C_aⁱ represents an antenna correlation of the channel between the cell i and the terminal.

11. The apparatus of claim 10, wherein the cell selector is configured to determine a quality metric for each cell, and the cell selection function determines the cell i having the largest quality metric.

12. The apparatus of claim 1, wherein the cell selector generates the cell selection based on the first estimates of the signal-to-interference ratio and the second estimates.

13. The apparatus of claim 1, wherein the apparatus is included in the terminal.

14. The apparatus of claim 1, wherein the first and second estimates are generated in the terminal, and the cell selector is included in at least one other entity in the communication system.

15. A method of cell selection in a communication system that includes a plurality of cells, wherein the cells transmit respective signals that include respective pilots through respective channels to a terminal, the method comprising:

generating first estimates of at least one of signal strengths and signal-to-interference ratios of signals received from respective cells;

generating second estimates of at least one of a frequency selectivity, a time selectivity, and an antenna selectivity of respective channels between the terminal and respective cells; and

selecting a cell based on the first estimates and the second estimates.

16. The method of claim 15, wherein generating second estimates of the frequency selectivity of a channel includes generating estimates of at least one of a coherence bandwidth and a delay spread of the channel.

17. The method of claim 16, wherein the signals are orthogonal frequency division multiplex signals and the second estimates are generated by calculating a correlation in signal strength between pilots at different frequencies and at a same time instant.

18. The method of claim 15, wherein generating second estimates of the time selectivity of a channel includes generating estimates of at least one of a Doppler frequency shift and a coherence time of the channel.

19. The method of claim 18, wherein the signals are orthogonal frequency division multiplex signals and the second estimates are generated by determining correlations in signal strength between pilots at different time instants and at a same frequency for respective cells.

20. The method of claim 15, wherein generating second estimates of the antenna selectivity of a channel includes generating estimates of an antenna correlation of the channel.

21. The method of claim 15, wherein the signals are orthogonal frequency division multiplex signals and the second estimates are generated by determining correlations in signal strength between pilots from different antennas at a cell and at same time instants and same frequencies.

22. The method of claim 15, wherein generating first estimates includes generating mean signal levels of pilots received from cells.

23. The method of claim 22, wherein generating first estimates includes filtering the mean signal levels generated.

24. The method of claim 15, wherein selecting the cell includes computing a cell selection function:

Cell=f(Sⁱ, T_dⁱ, F_Dⁱ, C_aⁱ)

for each cell, in which Cell represents a selected cell, Sⁱ represents a first estimate for a cell i, T_dⁱ represents a delay spread of the channel between the cell i and the terminal, F_Dⁱ represents a Doppler frequency shift of the channel between the cell i and the terminal, and C_aⁱ represents an antenna correlation of the channel between the cell i and the terminal.

25. The method of claim 24, wherein selecting the cell includes determining a quality metric for each cell, and the cell selection function determines the cell i having the largest quality metric.

26. The method of claim 15, wherein selecting the cell includes computing the cell selection based on signal-to-interference ratios and the second estimates.

27. The method of claim 15, wherein the method is carried out in the terminal.

28. The method of claim 15, wherein the steps of generating the first and second estimates are carried out in the terminal;

further comprising the step of communicating the first and second estimates to at least one other entity in the communication system;

the step of selecting the cell is carried out in the at least one other entity; and

further comprising the step of communicating the selected cell to the terminal.