question about HSDPA, code, CE

[paulus]

Hi all.. I have some questions which I want to make it clear..

1. In HSDPA, per cell max code is 15 codes..

If 15 codes==> 14.4 Mbps Throughput = (ChipRate/SF) x bits per Symbol x coding rate x Nb of code = (3,84x 10^6)/16 x 4 x 1 x 15 = 14,4 Mbps

We also have a setting : max HSDPA User, e.g 64 percell

The question is, 1 code is for how many users?

2. Then, by when the code is said : congestion?? Or, by when the code resource has been utilized 100%? Is there a theoretical theory which can explain this?

3. Okay, then, about CE.. How many CEs are used if we want to have throughput 14.4 Mbps, or 7.2 Mbps?


4. What's the different between 16 QAM (as HSDPA modulation) and 64 QAM (HSPA+ modulation).. Theoretically? Experience?

Thanks..

[elkador]

1) 1 Code at a given time, can be used by max 1 user. However if looking at a broader time, you can have some TTI multiplex. Meaning same code can be used by up to 3 different users
2) Code congestion : all codes are used (15) by users, so there is no code left for any additional users. It happens obviously after the downgrade of all users to their minumum numbers of codes in order to respect their minimum thxput granted.
3) depends highly on the vendor. NSN is typically requiring 72 CE for HSDPA allocation, and it is fixed reservation (for no users, or for 4 users reaching 14.4mbps, it will stay the same amount). there is also some additionnal CE required for signaling
4) 16 QAM : 15 codes use leads to 14.4mbps. 64QAM : 15 codes leads to 21mbps. You are simply able to send more bits with a given symbol rate. Real life : 64QAM requires an excellent signal (both RCSP and Ec/Io), this happens typically when you are close to the site (few hundred meters), and not so much traffic on it.

Thx & Rep are welcome

[chefo]

I would say 1 HS-PDSCH code can be assigned to 1 user for a specific TTI if there is only one HS-SCCH configured in the cell.

Multiple HS-SCCH can enable TTI multiplexing between more users.

Apart from this, the overall number of users served by this cell's HS-PDSCH is limited by the admission threshold.

The algorithm for assigning the TTIs between the users depends on the network settings, and can be RR (Round Robin), Proportional Fair with different level of "Fairness", and Best CQI.

More users in the of course would result in lower speeds.

About the CE - HSDPA doesn't use CE, it's performance depends on the hardware configuration of the BB unit (vendor dependent).

QPSK gives 2 bits/chip, 16QAM produces 4 bits/chip, 64QAM gives 8 bits/chip, hence the higher speeds with 64QAM. Switching between modulation orders happens at specific CQI thresholds i.e. depends on the channel quality: better the channel quality -> higher modulation order -> higher speed.

The congestion control can reduce the number of available SF16 codes as well as the available HS Power in the cell. Usually R99 services have higher priority, but this also is operator configurable.

15 HS-PDSCH codes are rarely seen allocated for HS service, it is possible only if the carrier is dedicated to HSDPA only. Normally you can have up to 14 codes if you have R99 and HSDPA on the same carrier/cell.

regards.

rep would be appreciated.

[paulus]

Hi all..

Thanks for giving your opinion.

Well, here I attach my summary about those related questions... I hope it's quite giving us for further discussions..


Pleas add my rep if you find this useful..

Thanks

BR/PCS

[nupong]

QPSK gives 2 bits/chip, 16QAM produces 4 bits/chip, 64QAM gives 8 bits/chip,

I could agree all the part except 64QAM should give 6 bits/chip (64=2^6)

[chefo]

miss-type, sorry