Efficient almost blank subframe allocation
A base station transmits a message to a plurality of wireless devices in connected mode. The message comprises a subframe allocation bitmap indicating a plurality of subframes. The plurality of subframes comprises a plurality of almost blank subframes. During majority of symbols of an almost blank subframe of a base station, no signal is transmitted by the base station or signals are transmitted at an almost blank subframe power level that is different from a transmit power during a non-almost blank subframe.
1. A method for use by a base station, the method comprising:
a) transmitting a message comprising a subframe allocation bitmap indicating a plurality of Almost Blank Subframes, said plurality of Almost Blank Subframes consisting of second, fourth, seventh, and ninth subframes of every radio frame in a plurality of radio frames; and
b) transmitting to a wireless device a unicast message comprising:
i) a first measurement subframe allocation bitmap indicating a first plurality of measurement subframes of a primary carrier, said first plurality of measurement subframes excluding said plurality of Almost Blank Subframes; and
ii) a second measurement subframe allocation bitmap indicating a second plurality of measurement subframes of said primary carrier, said second plurality of measurement subframes excluding any of the subframes in said first plurality of measurement subframes; and
wherein during a majority of symbols of an Almost Blank Subframe: signals are transmitted at an Almost Blank Subframe power level that is lower than a transmit power during a non-Almost Blank Subframe.
2. The method of claim 1 , further comprising transmitting during an Almost Blank Subframe, a common reference signal only in a control region.
3. The method of claim 1 , wherein each radio frame in said plurality of radio frames is assigned a system frame number (SFN) and is divided into N subframes, N being an integer greater than one.
4. The method of claim 1 , wherein said message further comprises:
a) a subframe allocation repetition period in terms of n radio frames, n being an integer greater than or equal to one; and
b) a subframe allocation offset i, i being an integer greater than or equal to zero.
5. The method of claim 4 , wherein said subframe allocation bitmap indicates a plurality of subframes in k frames, k being an integer and 1≦k≦n, said bitmap applying to subframes in k frames starting from frames whose SFN meets (SFN mod n=i) criterion.
6. The method of claim 5 , wherein n is equal to 2 j , and j is one of the following numbers: 0, 1, 2, 3, 4, and 5.
7. The method of claim 5 , wherein said base station broadcasts:
a) said system frame number represented by m bits;
b) the p most significant bits of said system frame number employing a plurality of subcarriers in the in the middle of a frequency band of a carrier; and
c) the (m-p) least significant bits of said system frame number by encoding control blocks in said physical broadcast channel over 2 (m-p) frames, sequential position of said encoded control blocks determining the (m-p) least significant bits.
8. A method for use by a base station, the method comprising:
a) transmitting a message comprising a subframe allocation bitmap indicating a plurality of Almost Blank Subframes, said plurality of Almost Blank Subframes consisting of third and eighth subframes of every radio frame in a plurality of radio frames; and
b) transmitting to a wireless device a unicast message comprising:
i) a first measurement subframe allocation bitmap indicating a first plurality of measurement subframes of a primary carrier, said first plurality of measurement subframes excluding said plurality of Almost Blank Subframes; and
ii) a second measurement subframe allocation bitmap indicating a second plurality of measurement subframes of said primary carrier, said second plurality of measurement subframes excluding any of the subframes in said first plurality of measurement subframes; and
wherein during a majority of symbols of an Almost Blank Subframe: signals are transmitted at an Almost Blank Subframe power level that is lower than a transmit power during a non-Almost Blank Subframe.
9. The method of claim 8 , wherein said unicast message further configures measurement subframes of a plurality neighboring carriers for said wireless device.
10. The method of claim 8 , wherein said wireless device periodically reports channel state information for subframes indicated in said first measurement subframe allocation bitmap.
11. The method of claim 8 , wherein said wireless device periodically reports channel state information for subframes indicated in said second measurement subframe allocation bitmap.
12. The method of claim 8 , further comprising transmitting during an Almost Blank Subframe, a common reference signal only in a control region.
13. The method of claim 8 , wherein each radio frame in said plurality of radio frames is assigned a system frame number (SFN) and is divided into N subframes, N being an integer greater than one.
14. The method of claim 8 , wherein said message further comprises:
a) a subframe allocation repetition period in terms of n radio frames, n being an integer greater than or equal to one; and
b) a subframe allocation offset i, i being an integer greater than or equal to zero.
15. The method of claim 14 , wherein said subframe allocation bitmap indicates a plurality of subframes in k frames, k being an integer and 1≦k≦n, said bitmap applying to subframes in k frames starting from frames whose SFN meets (SFN mod n=i) criterion.
16. A method for use by a base station, the method comprising:
a) transmitting a message comprising a subframe allocation bitmap indicating a plurality of Almost Blank Subframes, said plurality of Almost Blank Subframes consisting of second, fourth and eighth subframes of every radio frame in a plurality of radio frames; and
b) transmitting to a wireless device a unicast message comprising:
iii) a first measurement subframe allocation bitmap indicating a first plurality of measurement subframes of a primary carrier, said first plurality of measurement subframes excluding said plurality of Almost Blank Subframes; and
iv) a second measurement subframe allocation bitmap indicating a second plurality of measurement subframes of said primary carrier, said second plurality of measurement subframes excluding any of the subframes in said first plurality of measurement subframes; and
wherein during a majority of symbols of an Almost Blank Subframe: signals are transmitted at an Almost Blank Subframe power level that is lower than a transmit power during a non-Almost Blank Subframe.
17. The method of claim 16 , wherein said unicast message further configures measurement subframes of a plurality neighboring carriers for said wireless device.
18. The method of claim 16 , wherein said wireless device periodically reports channel state information for subframes indicated in said first measurement subframe allocation bitmap.
19. The method of claim 16 , wherein said wireless device periodically reports channel state information for subframes indicated in said second measurement subframe allocation bitmap.
20. The method of claim 16 , further comprising one of the following:
a) after a decrease in traffic load of said base station by an amount greater than a first value, transmitting a second message comprising a second subframe allocation bitmap indicating a second plurality of Almost Blank Subframes, said second plurality of Almost Blank Subframes consisting of second, fourth, seventh, and ninth subframes of every radio frame in a second plurality of radio frames; and
b) after an increase in traffic load of said base station by an amount greater than a second value, transmitting a third message comprising a third subframe allocation bitmap indicating a third plurality of Almost Blank Subframes, said third plurality of Almost Blank Subframes consisting of third and eighth subframes of every radio frame in a third plurality of radio frames.