Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2001-02-07
2004-05-25
Vo, Nguyen T. (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S063300
Reexamination Certificate
active
06741862
ABSTRACT:
BACKGROUND
We use the following acronyms in our discussion:
1xEV-DO
1xEV-Data Only
1xEV-DV
1xEV-Data and Voice
3GPP2
3
rd
Generation Partnership Project 2
BS
Base Station
CDMA
Code Division Multiple Access
CDMA-2000
A CDMA standard for voice and data
DRC
Data Rate Control
HDR
High Data Rate
IS-95
TIA/EIA Interim Standard 95
MS
Mobile Station
psd
Power Spectral Density
RA
Reverse Activity
RAE
Reverse Activity Bit
SIR
Signal-to-Interference Ratio
SNR
Signal-to-Noise Ratio
TDMA
Time Division Multiple Access
We use the following notations in our discussion.
a
i
path gain from the i-th sector to a MS
&agr;
R
relative data power over pilot for reverse rate R
b
i
path gain from a MS to the i-th sector
&bgr;
interference factor
d
R
minimum required E
b
/I
0
for reverse rate R
E
b
energy per bit
E
b
i
energy per bit for the i-th MS
F
base station noise figure
G
processing gain = W/R
g
i
path gain from the i-th MS to the BS
I
psd of interference from other sectors
I
0
psd of thermal noise and interference
I
0
i
psd of thermal noise and interference for the i-th MS
I
t
psd of the total received power at the BS
N
number of mobile stations in a sector
N
th
psd of thermal noise
P
i
pilot transmission power of the i-th MS
R
reverse rate
R
i
reverse rate of the i-th MS
S
received signal power
S
i
received pilot power of the i-th MS
W
system bandwidth
FIG. 1
shows a general configuration of cellular wireless communication systems. A large geographic area is divided into cells
10
. Each cell can be further divided into sectors
12
. Typically three sectors per cell are used as shown in the figure. We will use the term sector even when there is only one sector per cell. In each cell, a BS
14
,
20
,
22
serves three sectors and communicates with multiple MS's
16
,
18
in its cell.
High Data Rate (HDR) is an emerging mobile wireless access technology that enables personal broadband Internet services which can be accessed from anywhere, anytime. Developed by Qualcomm, HDR is a new air interface optimized for IP packet data services. HDR can deliver a shared forward link transmission rate of up to 2.4576 Mbit/s per sector using only (1×) 1.25 MHz of spectrum. HDR has been adopted by TIA as a new standard in the CDMA2000 family, an EVolution of the current 1×RTT standard for high-speed data-only (DO) services, formally referred to as 1×EV-DO or IS-856.
IS-856 defines AN, AT, and sector as follows:
Access Network (AN): The network equipment providing data connectivity between a packet switched data network (typically the Internet) and the access terminals. An access network is equivalent to a base station in the CDMA-2000 standard.
Access Terminal (AT): A device providing data connectivity to a user. An access terminal may be connected to a computing device such as a laptop personal computer or it may be a self-contained data device such as a personal digital assistant. An access terminal is equivalent to a mobile station in the CDMA-2000 standard.
Sector: The part of the access network that provides one CDMA channel.
We will use BS and AN interchangeably and MS and AT interchangeably.
In HDR, the forward-link channel is time-shared among MS's. Actual forward throughput becomes smaller than the instantaneous rates if there are more than one MS.
The MS periodically monitors the quality of its forward channels by measuring the forward-link SIR values from several sectors. The MS chooses the sector among active sectors whose SIR is the highest and calculates the maximum possible forward-link rate supported at this SIR. The MS then sends a DRC value in every slot (one slot is 1.66 msec) that indicates this rate to the BS. The following table shows the DRC value and the corresponding rate in Kbps. Packet length shows how many slots a forward packet needs at each rate.
Packet Length
DRC value
Rate (kbps)
in slots
1
38.4
16
2
76.8
8
3
153.6
4
4
307.2
2
5
307.2
4
6
614.4
1
7
614.4
2
8
921.6
2
9
1228.8
1
10
1228.8
2
11
1843.2
1
12
2457.6
1
In HDR, the reverse link (from MS to BS) can support bit rates 9.6, 19.2, 38.4, 76.8, and 153.6 Kbps in a 1.25 MHz spectrum (no overlap with the forward-link spectrum). Since the reverse link is shared using CDMA, these are the actual rates each MS can get.
A MS can communicate with several sectors. A MS is in soft handoff if decoding of the reverse packet is done at several sectors and an error-free frame, if any, is finally chosen. A MS is in softer handoff, if several sectors in the same cell jointly decode the reverse packet.
Due to the unpredictable nature of the reverse traffic and delay, it is difficult to schedule individual reverse traffic together at the BS. As we will show later, there is a limit on the aggregate reverse rate in each sector at which MS's can send data reliably. Therefore, it is important to be able to control the reverse rate of each MS so that their aggregate rate rarely exceed the limit. We briefly describe how this is done in HDR.
In HDR, there are four variables for reverse rate control, i.e., MaxRate, CurrentRate, CombindedBusyBit, and CurrentRateLimit. CurrentRate is the actual rate at which a MS sent data last time. The BS can send broadcast (to all MS's in the sector) or unicast (to a specific MS) RateLimit messages. After receiving the RateLimit message (unicast or broadcast), the MS sets its CurrentRateLimit equal to the RateLimit value. CurrentRateLimit is initially 9.6 Kbps.
The BS can send another broadcast control signal, RAB (reverse activity bit), to all active MS's. The MS collects all RAB's from active base stations and determines CombinedBusyBit. The CombinedBusyBit is 1 if any of these RAB's is 1 and is 0 otherwise. The MS then computes the MaxRate with a certain probability depending on the CombinedBusyBit. This probability is a function of both the CurrentRate and the CombinedBusyBit. The MS then chooses a rate that does not exceed either of MaxRate or CurrentRateLimit. The rate is also limited by the transmission power of the MS (in general more power is needed for transmitting at a higher rate). If the payload size is small enough to be transmitted using a lower rate, then the MS choose the lower rate. The following summarizes the reverse rate variables:
CurrentRateLimit
1. initially 9.6 Kbps
2. after receiving broadcast or unicast RateLimit message, an MS updates it as follows:
a. if the RateLimit<=CurrentRateLimit, set CurrentRateLimit=RateLimit immediately.
b. if the RateLimit>CurrentRateLimit, set CurrentRateLimit=RateLimit after one frame (16 slots).
CombinedBusyBit
1 if and only if any RAB is 1 from any sector.
MaxRate
2.0*CurrentRate if CombinedBusyBit=0 and with probability x.
0.5*CurrentRate if CombinedBusyBit=1 and with probability x.
MaxRate cannot be set to 0 in any case.
MaxRate cannot exceed 153.6 Kbps.
MS selects a transmission rate (becomes CurrentRate) such that
1. rate<=MaxRate
2. rate<=CurrentRateLimit
3. rate<=highest rate that can be accommodated by the transmission power
4. rate<=highest rate such that the number of minimum payload bits is less than the number of bits to send.
Default values of the transition probability x are:
CombinedBusyBit
CurrentRate
MaxRate
Default probability
0
9.6
kbps
19.2
kbps
0.75
0
19.2
kbps
38.4
kbps
0.25
0
38.4
kbps
76.8
kbps
0.125
0
76.8
kbps
153.6
kbps
0.125
1
19.2
kbps
9.6
kbps
0.25
1
38.4
kbps
19.2
kbps
0.25
1
76.8
kbps
38.4
kbps
0.5
1
153.6
kbps
76.8
kbps
1
SUMMARY
In general, in one aspect, the invention features a method that includes (a) at a mobile wireless communication device operating in a cell, transmitting data to sectors, and (b) at the base station controlling the reverse data rate of the mobile device based on an estimated amount of interference the mobile device is causing to other sectors. Implementations of the invention may include one or more of the following features. The estimated amount of interference is based on a forward-link SIR for the mobile device. The forward-link SIR is averaged over a peri
Chung Sae-Young
Kim Dae-Young
Airvana, Inc.
Fish & Richardson P.C.
Smith Sheila B.
Vo Nguyen T.
LandOfFree
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