Dynamic code allocation for downlink shared channels

Details Dynamic code allocation for downlink shared channels Dynamic code allocation for downlink shared channels

1999-03-16

2004-02-17

Bocure, Tesfaldet (Department: 2631)

Pulse or digital communications

Spread spectrum

Direct sequence

C375S146000, C375S147000, C375S377000, C370S335000

Reexamination Certificate

active

06693952

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to communications and, more particularly, to wireless communications systems.
BACKGROUND OF THE INVENTION
With the urge to provide multimedia capabilities in mobile communications, there is an increasing need for providing higher bandwidth in a wireless access network. Thus, multi-rate and variable rate services are considered very important features in future wireless systems such as the Universal Mobile Telecommunications System (UMTS) (e.g., see E. Dahlman et al, “
UMTS/IMT
2000
Based On Wideband CDMA
,” IEEE Communications Magazine, September 1998, pp 70-80). In proposed UMTS-based Terrestrial Radio Access (UTRA) FDD (frequency division duplex) systems, different data rates are achieved by using, what is known in the art as, channelization codes with different spreading factors. (As used herein, the term “data rate” applies to any multi-media application that requires packet transport, e.g., a voice packet is transmitted with a particular data rate.)
Channelization codes in UMTS are Orthogonal Variable Spreading Factor (OVSF) codes that preserve the orthogonality between downlink channels of different data rates and spreading factors within a cell. (As known in the art, in wireless communications a geographical region is divided into cells (typically of a hexagonal pattern).) The OVSF codes (hereafter simply referred to as codes) are defined using a code-tree, a portion of which is shown in FIG.
1
. As shown in
FIG. 1
, a particular code is represented as Ci,j, where the subscript i,j, identifies the length spreading factor (SF) and the number of the code, respectively. For example, C
2
,
1
is the first code with a length SF of 2. As such, it can be observed that each level of the code-tree defines a number of codes having a particular length SF. In the context of
FIG. 1
, for an illustrative chip rate of 4.096 Mcps (millions of chips per second), a mobile data user (user) requiring a data rate of 512 Kbps (thousands of bits per second) will use a code with a spreading factor of 8 (either one of C
8
,
1
through C
8
,
8
) while a 64 Kbps user uses a code (further down the tree) with a spreading factor of 64 (either one of C
64
,
1
through C
64
,
64
) (not shown).
Unfortunately, all codes within the code-tree cannot be used simultaneously within a cell. In particular, a code can be used in a cell if and only if no other code on the path from the specific code to the root of the tree or in the sub-tree below the specific code is used in the same cell. For example, with reference to
FIG. 1
, if the code C
4
,
3
is used, then the codes C
1
,
1
, C
2
,
2
, and all codes corresponding to the children of the node representing the code, C
4
,
3
, cannot be used. Thus, the number of available codes depends on how the codes are assigned to each user.
The downlink shared channel (DSCH) concept (e.g., see Tdoc SMG2 UMTS-L1 311/98
, “UTRA FDD Downlink Packet Data Operation with Shared Channels
”, Nokia) is an attempt to remedy this potential code shortage problem. In DSCH, all codes are shareable, or multiplexed, between users on a frame by frame basis, thus achieving the highest possible multiplexing gain.
In particular, DSCH is a type of transport channel shared by a number of users for data rate transmissions in which the generated traffic is usually bursty and delay insensitive (such as results from web browsing). As such, DSCH only carries data traffic from high-rate users. A user is assigned a temporary code for the DSCH. The assigned code is on a frame-by-frame basis. A user therefore uses the assigned code for at least a full 10 ms (milli-second) frame. Each user who will share the DSCH is assigned a dedicated downlink traffic channel. (This dedicated traffic channel carries Layer
1
information such as pilot, power control bits (TPC) and transport-format combination indicator (TFCI) bits. This channel can also carry higher layer (Layer
2
/
3
) signaling.)
SUMMARY OF THE INVENTION
However, we have observed that the above-described code sharing method generates additional Layer
1
,
2
, and
3
signaling since the code assignments may need to be reshuffled to admit new users. For example, as noted above, the code assigned to a low data rate user eliminates possible assignments of any code on the path back to the root of the code-tree (these are codes with lower length SFs than the assigned code). As such, in order to free up a code (with a lower length SF) for use by a high data rate user, a low rate user may have to be reassigned another code.
Therefore, and in accordance with the invention, a code-tree is partitioned into two parts, or sets: a permanent set and a shared set.
In an embodiment of the invention, a code-tree is partitioned into two sets: a permanent set and a shared set. Those codes in the permanent set are assigned to a user for the duration of a session, or connection. Those codes in the shared set are assigned to users on a frame-by-frame basis using the above-mentioned DSCH channel. Typically, users with low data rate requests (e.g., voice) are assigned codes from the permanent set, and users with high data rate requests are assigned codes from the shared set.
In another embodiment of the invention, the partition boundary between the permanent set and the shared set is dynamically shifted based on traffic conditions.


REFERENCES:
patent: 6091757 (2000-07-01), Cudak et al.
patent: 6108369 (2000-08-01), Ovesjo et al.
patent: 6163524 (2000-12-01), Magnusson et al.
patent: 6233231 (2001-05-01), Felix et al.
patent: 2002/0018457 (2002-02-01), Choi et al.
patent: 2002/0051437 (2002-05-01), Take
patent: WO-00/49816 (2000-08-01), None
Adach et al., “Tre-structured generation of orthogonal spreading codes with different lengths for forward link of DS-CDMA mob radio,” Electronic letter, 2ndJan. 1997, vol. 33, No. 1, 27-28.*
Minn et al., “Dynamic Assignment of Orthogonal Variable-Spreading Factor does in W-CDMA,” IEEE, 2000, pp 1429-1440.*
Shueh, “Code Assignment for IMT-2000 on Forward Radio Link,”IEEE, 2000, pp906-910.*
Tseng et al., “Code Palcment and Replacment Strategies for Wideband CDMA OVSF Code-Tree,” IEEE, 9/01 2001, pp 562-566.

Affiliated with

Also associated with

Rating

Dynamic code allocation for downlink shared channels does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Dynamic code allocation for downlink shared channels, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dynamic code allocation for downlink shared channels will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3284009