Friday, 27 February 2009

Dual-Cell HSPA in Release 8 and beyond

Some interesting developments are ongoing in the 3GPP standardisation from Release-8 onwards. You must be aware that the current bandwidth in UMTS/HSPA is 5 MHz. Since most of the operators generally won bigger chunk of spectrum of contiguous 5MHz band, they can actually combine these chunks to create a larger spectrum and hence increase data rates.

In Release 8 in downlink, it is possible to increase data rates using either a combination of MIMO and 64QAM or dual-cell HSDPA for operation on two 5MHz carriers with 64QAM, data rates reach up to 42Mbps.

In deployments where multiple downlink carriers are available, the new multicarrier operation offers an attractive way of increasing coverage for high bit rates. Rel-8 introduces dual-carrier operation in the downlink on adjacent carriers. This technique doubles the peak rate from 21Mbps to 42Mbps without the use of MIMO – it doubles the rate for users with typical bursty traffic; therefore, it also doubles the average user throughput, which translates into a substantial increase in cell capacity.

You may remember that I mentioned earlier that the operators are not too keen on going for MIMO for non-LTE technology. This is because they will have to upgrade their hardware and the antennas which could increase their cost significantly for a technology that is not going to be around for long.

Another thing to note before it becomes too confusing is that there are two terms for 'DC' being used right now. One of them is 'Dual Carrier' and other is 'Dual Cell'. In Release 8, the term being used is Dual-Cell for HSDPA which is also known as DC-HSDPA. The Technical specification to follow is 3GPP, TR 25.825 “Dual-Cell HSDPA operation” V1.0.0, May 2008.

The Dual-Cell assumes that both the 5MHz bands are contiguous. If they are not then the better term to refer for DC is Dual-Carrier.

A dual-carrier user can be scheduled in the primary serving cell as well as in a secondary serving cell over two parallel HS-DSCH transport channels. All non-HSDPA-related channels reside in the primary serving cell, and all physical layer procedures are essentially based on the primary serving cell. Either carrier can be configured to function as the primary serving cell for a particular user. As a consequence, the dual-carrier feature also facilitates an efficient load balancing between carriers in one sector. As with MIMO, the two transport channels perform hybrid automatic repeat request (HARQ) retransmissions, coding and modulation independently. A difference compared to MIMO is that the two transport blocks can be transmitted on their respective carriers using a different number of channelization codes. In terms of complexity, adding a dual-carrier receiver to UEs is roughly comparable to adding a MIMO receiver. Because the two 5MHz carriers are adjacent, they can be received using a single 10MHz radio receiver, which is already be available if the UE is LTE-capable.

Following the introduction in Release 8 of dual-carrier operation in the downlink, 3GPP is now discussing operation on multiple 5MHz carriers. Multiband operation of multiple carriers allows a single user to simultaneously aggregate and use the spectrum distributed over different bands. This gives operators greater fl exibility when using available spectrum. Increasing the number of carriers that UEs receive from two to four doubles the peak rate and achievable user throughput. For bursty traffic, this translates into substantially greater capacity, either as a larger number of users at a given data rate, or as a higher data rate for a given number of users. To substantially boost spectral effi ciency, 3GPP is studying the combination of dual-carrier operation and MIMO with 64QAM in the downlink, thereby doubling the peak data rate to 84Mbps. Similarly, they are studying the combination of MIMO, 64QAM and up to four downlink carriers to support peak data rates of more than 100Mbps. The support for UE reception on two frequency bands is an enabler to DC-HSDPA for operators who do not have adjacent 5MHz carriers available in one band, and is therefore of key importance for the further evolution of multi carrier HSPA.

As a consequence of increased data rates in downlink, the uplink data rates need to be improved too. From the aggregation of multiple FDD downlink carriers, the paired FDD uplink carriers can be utilized for improved uplink transmissions. 3GPP studies the usage of two adjacent 5MHz carriers for dual carrier uplink transmissions (DC-HSUPA) supporting data rates of up to 23Mbps. A further benefit of utilizing two uplink carriers is the possibility to support more efficient load balancing in the uplink direction.

In summary, uplink multicarrier operation increases availability as well as coverage of high data rates in the uplink.

In Conclusion, Rel-8 defines improvements in HSPA to achieve higher rates through dual carrier or combined 64QAM+MIMO operation. With the Rel-8 specification nearing completion (targeted for March 2009), planning is already under way in 3GPP for Rel-9 and Rel-10. Further multi-carrier and MIMO options are being explored for HSPA in Rel-9 and Rel-10

If you want to explore this topic further see:

14 comments:

Tiago Junqueira said...

Will HSPA be able to be proposed to IMT Advanced as a 4G technology? Together with 802.16m and LTE-advanced

Zahid Ghadialy said...

I dont think HSPA can meet the IMT-Advanced requirements. There is a maximum rate (not sure how much) that HSPA can go to and its falls far behind the requirements.

I also think that there will ultimately a limitation because of WCDMA as its not very efficient over very wide bandwidths.

Ravi said...

Hi, A very basic doubt. While using MIMO or DC HSDPA, does the network send same or different data packets over the 2 links?

Zahid Ghadialy said...

For DC-HSPA different. For MIMO could be the same or different but generally different.

Ravi said...

Ok. For MIMO, does it mean effectively no data rate increase when "same" data is sent. Why would we want to send data then? Does it not become an overhead in such a case?

Zahid Ghadialy said...

Same data is sent for diversity to achieve reliability. I would encourage that you read Agilent's paper on MIMO here.

harry said...

could you please provide the link to DC-HSPA study material?

Zahid Ghadialy said...

Hi Harry,

Please see the links embedded in the post as they will give you an idea about DC-HSPA.

Regards!

harry said...

Hi Zahid,

These links are related to DC-HSDPA.
But I am interested in DC-HSUPA. could you please let me know the link for its TR in 3GPP and other papers related to DC-HSUPA?

Many Thanks,
Harry

Zahid Ghadialy said...

Hi Harry,

Sorry I misunderstood. I havent read much about DC-HSUPA. Infact it would probably be called DC-E-DCH. Earlier I had heard about 25.317 but didnt find it on server. Once I have more Info, I will blog about it.

Regards,
Zahid

Anonymous said...

Dear Sir,

Good Explanation. Recently I have come across some information that DC-HSDPA has some limitations practically in Code Assignment for a Dual Cell User. Apparently current hardware provided by all vendors have some limitation.
I dont have much information & need your guidance please

SOUMITRI said...

on which condition RRC reestablishment happens in DC-HSDPA?

Anonymous said...

Are there spec which mention the DPCH frame offset in Dual cell?

Hossein zarei said...

Hi,

Can DigRF 3.09 (312Mhz) support the DC-HSDPA in release.8?
8bits*2(I and Q)*15.36Mhz=245.7Mbps+Overhead should be less than 312MHz interface?