GB2479713A - A transmitter needs to identify itself only if it transmits to a receiver that is intentionally common - Google Patents

Abstract

The use of scrambling codes (SCs) by transmitters in code division multiple access (CDMA) communications enables different signal sources to be separable at the receiver. Hence, in an uplink, a mobile station (MS) must use its unique SC, so that a base station (BS) can separate the signals of all MSs being served. But, in downlink, the BS intentionally transmits user channel only to a selected MS, so there is no need for the BS to identify itself on downlink user channels. Instead, the BS uses the SC of the individual MS to which it transmits the user channel, allowing the BS to transmit one full set of channelization codes (CCs) to an individual MS in downlink. The BS transmitter only needs to identify itself using its unique SC to scramble the common signaling channels to MSs as they are intentionally common receivers of these common channels.

Description

New Theory on Scrambling to Eliminate Capacity Limitation Applicable to all CDMA based communications factor of 128 will typically output 125 CC, each with a theoretical user data rate between 21-25 Kb/s. The maximum number of CC are available when a spreading factor of 512 is used, with user data rate between 1-3 Kb/s per CC, while the minimum number of CC are available when a spreading factor of 4 is used with a data rate of up to 936 Kb/s per CC theoretically. A high value of spreading factor gives a high number of available CC, but the data rate of each channel is reduced in the same proportion. In other words either we can have large number of low data rate channels or small number of high data rate channels. The maximum data rate can be achieved by using a spreading factor of 4 out of which only 3 CC can be used for data. But considering other practical factors the maximum data rate available in downlink for Release 99 is approx 2 Mb/s per BS, which will also be considered in this paper for simplicity. In uplink a Mobile Station (MS) can use spreading factor of 4 and all the 3 CC, while another MS can also use a spreading factor of 4 and can get the same set of CC.

This is due to the fact that every MS has its own unique SC and each of them can use a full set of CC in uplink. In downlink, every BS uses its own unique SC and it can only transmit one full set of CC giving a maximum of 2 Mbis per cell to he shared between all MS in that cell. This behaviour of BS in downlink is similar to that of MS in uplink although the later transmits to a common receiver, while the former transmits intentionally to an individual receiver, The need for BS to use its unique SC for downlink user channels limits the whole cell Keywords-Base Station Cell BSi; (iiannelistaion Codes (CC); capacity to 2 Mb/s. This was investigated and became the base code Division Multiple Access (CDMA); down/ink; High-Speed for a new theory that eliminates the current capacity limitation.

Downlink Packe Access (HSDP.4); Mobile Station (MS); Orthogonal Variable Spreading factor (OVSF); Scrambling Code IL CURRENT CAPAcITY LIMITATION (SC); Uplink; Wideband Code Division Miikiple Access (WcDMJ() A. Exisfing Coding Technique for Downlink I. INTRODUCTION A BS ansmits signal intentionally to a single MS, but the In a Wideband Code Division Multiple Access (WCDMA) MS unintentionally get signals from neighbouring BS.

network Channelization Codes (CC) are used in Llownlink to Therefore, the MS is an unintentional common receiver of separate channels or users and Scrambling Code (SC) is used to many BS, but the existing technique actually eats the MS as separate the Base Station Cell (B S). There is a limitation on the an intentional common receiver. This puts a requirement on BS availability of CC due to the finite number of Orthogonal to identify itself in downlink user channels using its unique SC, Variable Spreading factor (OVSF) codes. In downlink a thus limiting it to ansmit only one set of CC as shown in Fig. spreading factor between 4 and 512 is used depending upon the 1.

requirement of number of channels and data rate. A spreading Ill, PROPOSED SOLUTION A. New Theoiy A transmitter needs to identify itself only if it transmits to a receiver which is intentionally common.

B. implementation of New Theory on WDMA Network In uplink the BS is a common receiver of all MS being served by the cell. So, it's correct for the MS to identify themselves using their unique SC, so that the BS can separate their signals. But in downlink the BS intends to transmit user channel only to a selected MS, although the MS do get unwanted signals from neighbouring BS. So, there is no need for the BS to identify itself on downlink user channels. Instead, the BS should use the SC of individual MS to which it transmits the user channel as shown in Fig. 3, This will allow the BS to transmit one full set of CC to an individual MS in This concludes that both the MS and BS use their unique downlink. The BS can still use its unique SC to scramble the SC while transmitting. It's justified in uplink for the Mobile common signalling channels to MS as they are intentionally Station (MS) to use its unique SC, as there are a number of MS common receiver of these common channels. Additionally, the transmitting to a common BS as shown in Fig. 2. But, it's not MS must have separate SC for UL and DL. So, that in DL justitied for the BS in downlink to use its unique SC for user other BS don't receive the transmitting BS's signal. A BS must channels as it transmits to a MS, which intentionally is not a only receive signals that are scrambled with UL SC of MS.

common receiver for many BS. Similarly, a MS must only receive signals that are scrambled with its DL SC. Finally, there needs to he two SCs per MS for UL/DL user channels and one SC per BS for DL common signalling channels.

B. Current (apacip' Limitation in Downlink The BS in downlink behaves similar to an individual MS in uplink although it doesn't intentionally transmit user channels to a common receiver. Now, if it has to transmit 3 channels to a MS using a spreading factor of 4, then it's left with no more C'. Eliminatio, of C'apacity Limitation CC for other MS in the cell as shown in Fig. 1. Although the If there is just one MS under a BS, then it can use full set of same CC can be used with another SC, but as the BS has to CC in downlink and get up to 2 Mb/s. But when other MS join identify itself it uses a unique SC and can only transmit one set this BS, then the available bandwidth is shared between them.

of CC. In proposed theory, the BS uses the SC of the individual MS to The limitation exists for downlink user channels due to the scramble the downlink user channels. Therefore the number of fact that the BS uses its unique SC. The limitation of available available SC for downlink user channels will be equal to the number of CC, limits the number of available channels, data number of MS under the BS. The BS can then transmit a full rate and users in the downlink. Due to this there is only one set set of CC to each MS scrambled by their individual SC. This of CC available in downlink limiting the cell capacity to 2 implies that, with the implementation of new theory the Mb/s to be shared among all available MS in the cell. WCDMA capacity can go up to 2 Mb/s per user instead of 2 Mb/s per cell. Obviously this can go up to 14.4 Mb/s per user 2) MS-I then informs BS-l that it has detected a strong instead of per cell with HSDPA, signal from BS-2 with CCI. It also informs the BS that it uses scrambling code SC 1.

P. lnra-ell inteiference 3) BS-l then sends a handover request to RNC with all the The implementation of this new theory won't cause any details i.e. the SC of MS and neighbour's BS ID and CC.

intra-cell interference. In a cell the SC is unique to an individual MS. The MS will reject all user channels which are 4) The RNC asks BS-2 to transmit CCI scrambled with not scrambled with its unique SC as shown in Fig. 4. Sc!.

5) The MS can now be connected to BS-2 with CC! scrambled with SC 1. This will complete the handover process.

F. Inter-Ce/I Interference As the MS in the neighbouring BS won't use the same SC, there won't be any intra cell interference due to the implementation of new theory. The MS will again reject all IV. CONCLUSION user channels from neighbouring BS that are not scrambled with its unique SC as shown in Fig. 5. This new proposal will prove to be a breakthrough for standardizing bodies, equipment providers and network operators who are still struggling to provide high bandwidth fairly to all available users. If this theory is practically proven then it will make it possible to provide a throughput above 10 Mb/s with HSDPA, without further up gradation to 4G and beyond. This paper will also open a debate on the basic concepts of CDMA and a broader discussion on the topic will further provide an opportunity to perform a greater degree of analysis. This paper is expected to be reviewed and discussed with feedback providers. A prototype based on this new theory can be developed and tested and the findings can be used to define a clear new standard for scrambling techniques and its implementation to gain the much required network capacity.

F. Inter-Cell Han dover Handover can be performed as shown in Fig. 6 and as described below: 1) MS-i currently connected with BS-l senses a strong signal CC! from BS-2. Obviously CCI will be scrambled using 5C2 or any other SC but not SC1 which is unique to MS-

Claims (4)

1. Cilaim New Theory on Scrambling to Eliminate Capacity Limitation New theory: A transmitter needs to identify itself only if it transmits to a receiver which is intentionally common.Amendments to the Claims have been filed as follows: Daim Existing theory 1. Currently transmitters identify themselves using a scrambling code (SC).
2. 2. There is no need for a transmitter to identify itself, if it's transmitting to a receiver which also receives signals unintentionally from other transmitters.
3. 3. This concept can be understood by the below example of a WCDMA network.A Base Station (BS) transmits signal intentionally to a single Mobile Station (MS). but the MS unintentionally receives signals from neighbouring BSs. Therefore, the MS is an unintentional common receiver of many BSs, but the existing technique actually treats the MS as an C intentional common receiver. This puts a requirement on BS to identify itself in downlink user (\J channels using its unique SC, thus limiting it to transmit only one set of channelization code (CC) per cell.New theory statementA transmitter needs to identify itself only if it transmits to a receiver which is intentionally common.New theory description1. This claim questions the use of SC by BS in downlink user channels.2. The BS should use the SC of individual MS to which it transmits the user channel.3. This will allow the BS to transmit one full set of CC to an individual MS in downlink, thus providing each MS a capacity equal to each cell.
4. 4. The BS can still use its unique SC to scramble the common signaling channels to MS as it's intentionally a common receiver of the signaling channels from multiple BSs.