Method and means for determining a handover in a radio communication system

• US 6,473,614 B1
• Filed: 12/17/1999
• Issued: 10/29/2002
• Est. Priority Date: 12/18/1998
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonktiebolaget L.M. Ericsson
• Inventors: Quensel, Joakim, Ljung, Petter
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): Iqbal, Khawar
• Application Number:
  US09/465,768
• Time in Patent Office: 1,047 Days
• Field of Search: 455/522, 455/69, 455/70, 455/13.4, 455/427, 455/436, 455/456, 455/438, 455/437, 455/561, 455/422, 455/442, 455/443, 455/375, 455/331, 455/332, 455/333
• US Class Current: 455/436
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data

Abstract

The present invention relates to methods and means for determining handovers in a cellular radio communication system. Power-budgets for a serving and a target cell are calculated (301,302). A ranking value for both cells is determined from the power-budgets (306,307). A new ranking value for the target cell is calculated (309) by adding a specific adjustment value, dependent on the BER in the serving cell and the target cell and derived from a communication-quality table, to the ranking value of the target cell. A handover is performed if the new ranking value exceeds the ranking value of the serving cell.

Claims

1. A method in a radio communication system for determining a handover of a connection (C1) established between a radio unit (100) and a first base station (101) to a second base station (105), where said first base station (101) is serving a serving cell (102) and said second base station (105) is serving a neighbouring cell (103), said method comprising:

a) measuring (301) of a first received signal strength (RSS_S) from said first base station (101);

b) measuring (302) of a second received signal strength (RSS_Nx) from said second base station (105);

c) measuring (303) at least a first (RXQUAL_S(RU)) and a second (RXQUAL_S(BTS)) communication-quality value in said serving cell (102);

characterised in said method further comprising;

d) calculating (306) a first power budget (pdgt_S) for said serving cell (102) from said first received signal strength (RSS_S);

e) calculating (307) a second power budget (pbgt_Nx) for said neighbouring cell (103) from said second received signal strength (RSS_Nx);

f) determining (306, 307) a first ranking value (RANK_S) for said serving cell (102) based on said first power budget (pdgt_S) and a second ranking value (RANK_Nx) for said neighbouring cell (103) based on said second power budget (pbgt_Nx);

g) calculating (309) a new ranking value (RANK_Nx(new)) for said neighbouring cell (103) from said second ranking value (RANK_Nx), wherein said new ranking value (RANK_Nx(new)) is calculated (309) by adding a communication-quality adjustment value (RxQual_X(Adj)) to said second ranking value (RANK_Nx);

h) determining (310) if said new ranking value (RANK_Nx(new)) exceeds said first ranking value (RANK_S);

if so, perform a handover (312) of said connection (C1) from said first base station (101) to said second base station (105).

2. The method as claimed in claim 1, wherein said communication-quality adjustment value (RxQual_X(Adj)) is calculated (308) from one of said two communication-quality values in said serving call (RXQUAL_S(RU), RXQUAL_S(BTS)) and a stored communication-quality value (RXQUAL_Nx) previously measured for said neighbouring cell (103).

3. The method as claimed in claim 2, wherein said communication-quality adjustment value (RxQual_(Adj)) is calculated (308) with the help of an adjustment algorithm.

4. The method as claimed in claim 3, wherein said adjustment algorithm includes a first (Cf(RXQUAL_S,RXQUAL_Nx)) and a second (Cf(RXQUAL_S,U)) compensation factor.

5. The method as claimed in claim 4, wherein said compensation factors (Cf(RXQUAL_S,RXQUAL_Nx), Cf(RXQUAL_S,U)) are derived from at least one table (table 1) defining said compensation factors in dependence of a number of different communication-quality values for said serving cell (RXQUAL_S(RU), RXQUAL_S(BTS),) and corresponding communication-quality values (RXQUAL_Nx, U) for said neighbouring cell.

6. The method as claimed in claim 5, wherein said compensation factors (Cf (RXQUAL_S,RXQUAL_Nx), Cf(RXQUAL_S,U) ) in said table (table 1) are updated at predetermined intervals.

7. The method as claimed in claim 3, wherein said adjustment algorithm also includes a function of time (f(t)) that starts at 1 and decreases to 0 after a predetermined time (T_m).

8. The method as claimed in claim 3, wherein said adjustment algorithm also includes a function of time and speed (f(t,v)) that starts at 1 and decreases to 0 after a predetermined time (T_m) and dependent on said speed (v).

9. The method as claimed in claim 1, wherein said communication-quality adjustment value (RxQual_X(Adj)) is calculated (308) from one of said two communication-quality values in said serving cell (RXQUAL_X(RU), RXQUAL_X(BTs)) and a predetermined communication-quality value (U) for said neighbouring cell (103).

10. The method as claimed in claim 1, wherein said communication-quality values (RXQUAL_S(Ru), RXQUAL_S(BTS), RXQUAL_Nx) are the bit error rate (BER_S,BER_Nx).

11. The method as claimed in claim 1, wherein said first ranking value (RANK_S) is set to the same value as said first power budget (pbgt_S) and said second ranking value (RANK_Nx) is set to the same value as said second power budget (pbgt_Nx).

12. An arrangement in a radio communication system for determining a handover between a serving cell and a neighbouring cell, characterised in that said arrangement comprises:

means for calculating (701) a first power budget for said serving cell and a second power budget for said neighbouring cell based on measured received signal strengths in said cells;

means for determining (702) a first ranking value from said first power budget and a second ranking value from said second power budget;

means for calculating a new ranking value (701) for said neighbouring cell based on said second ranking value and a communication-quality adjustment value (RxQual_X(Adj)), wherein said communication-quality adjustment value (RxQual_X(Adj)) is dependent on a measured communication-quality (RXQUAL_S, RXQUAL_Nx, U) in said serving and neighbouring cell;

means for determining (703) if said new ranking value exceeds said first ranking value and, if so, selecting said neighbouring cell as a target cell; and

means for initiating a handover (704) to said target cell.

13. The arrangement as claimed in claim 12, wherein said communication-quality adjustment value (RxQual_X(Adj)) is further dependent on a function of time (f(t)).

14. The arrangement as claimed in claim 13, wherein said function of time (f(t)) starts at 1 and decreases to 0 after a predetermined time (T_m).

15. The arrangement as claimed in claim 12, wherein said dependency of said communication-quality of said serving and neighbouring cell is defined in a communication-quality compensation table (table 1).