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Understand WLAN Offload

Wednesday, 30 January 2008

Comparison: HSPA+ vs LTE


Advantages of LTE over HSPA+
  • Flexible Spectrum usage possible with LTE: LTE will be the same whether the bandwidth available is 5MHz or 20MHz. Ofcourse the data rate will increase when the BW is increased. With HSPA+ only 5MHz bandwidhts possible. Similalrly with HSPA+ only FDD mode of operation is possible whereas with LTE FDD or TDD mode is possible.
  • Spectrum Effeciency: Better spectrum effeciency, by a factor of 2 atleast over HSPA+
  • Simpler Architecture: LTE has a much simpler and relatively flat architecture compared to the legacy UMTS network in HSPA+
  • Higher Data Rates: LTE gives DL data rates of 144Mbps and UL of 57Mbps. HSPA+ gives 42Mbps in DL and 11Mbps in UL
  • Ultra Low Latency: 10ms instead of 50ms for HSPA+
  • Short TTI: 0.5ms instead of 2ms for HSPA+

Advantages of HSPA+ over LTE
  • Will be ready much before LTE: HSPA+ technology should be available in Q1 2009 whereas the earliest with LTE would be sometime in 2010.
  • Much less investment in infrastructure: Since HSPA+ is evolution of HSPA which is already being deployed, it would be easier and less costly to upgrade. With LTE since its based on OFDM a lot of new components will be required. Also in case of LTE the number of components are reduced but since they work in a different way, new components will be required.
Did i miss something?

5 comments:

Sundararaman said...

Zahid,
Thanks so much for the very useful info. Just out of curiosity, can multi-carrier HSPA+ be a good competitor for LTE? Vodafone had been proposing this for a while.

I am wondering if my following calculations are correct. Based on the information, a HSPA+ 4x multi-carrier for 5*4=20Mhz can come close to providing 42*4= 168Mbps on downlink which is over the LTE capacity for 20Mhz.

It seems like multi-carrier HSPA+ can just do what LTE is proposing and at the same time avoid costly infra-structure revamp on the network side. What is your take on this?

Also, what does better spectrum efficiency mean for LTE? Does it have anything to do with MIMO that LTE supports and HSPA does not?

Thanks,
Shiva

Zahid Ghadialy said...

>> Just out of curiosity, can multi-carrier HSPA+ be a good competitor for LTE? Vodafone had been proposing this for a while.

A: HSPA+ will be a good competitor to LTE for some time to come. Operators who have already deployed HSPA based solution will not move to LTE as long as possible to avoid disruption to service and ofcourse to save cost. Also at present the number of users using Packet data using mobiles have to exceed a certain threshold before they would think about this move.

I should also point this out though that in UK and US lots of operators are offering cheap unlimited data plans using Mobile data cards. If there is a lot of demand then operators may be forced into LTE much earlier then they would like to.

>> I am wondering if my following calculations are correct. Based on the information, a HSPA+ 4x multi-carrier for 5*4=20Mhz can come close to providing 42*4= 168Mbps on downlink which is over the LTE capacity for 20Mhz.

>> It seems like multi-carrier HSPA+ can just do what LTE is proposing and at the same time avoid costly infra-structure revamp on the network side. What is your take on this?

A: HSPA+ uses the same 5MHz bandwidth as in case of WCDMA. Flexible BW is not possible with HSPA+. The main reason for 5MHz as far as i remember is because if the BW goes beyond 5MHz, Multipath Interference (a.k.a. MPI) increases and this can actually deteriorate the signal quality received, especially when HOM are employed (as in HSPA+). This is the reason OFDM was used in case of LTE (and WiMAX and all other new technologies) as it is immune to this MPI. Also because in case of OFDM many frequencies are used and this has small granualarity they can be rearranged to create flexible bandwidth. This is not possible with WCDMA

>>Also, what does better spectrum efficiency mean for LTE? Does it have anything to do with MIMO that LTE supports and HSPA does not?

A: Wikipedia says: Spectral efficiency or spectrum efficiency refers to the amount of information that can be transmitted over a given bandwidth in a specific digital communication system.

In case of HSDPA over 5MHz we can transmit maximum of 14.4 Mbps. With HSPA+ the data rates can be increased upto 42 Mbps so the spectrum effecincy is nearly 3


Ps: My low level technical terminology is quite rusty, if someone can explain it better then please do.

Anonymous said...

The main reason why LTE is better than HSPA+ is that LTE is scaleable, as far as bandwidth is concerned. Therefore it offers operators more felibility and tailoring of resources.

AG said...

when you carry 14.4 Mbps in 5 MHz bandwidth, the spectral efficiency is 14.4/5=2.88 bps/Hz
When you increase the bit rate over the same bandwidth, you increase the spectral efficiency. But the spectral efficiency is not the ratio of improvement [no unit]. It is the bitrate over bandwidth, measured in bit per second and per Hertz.

ankushkrishna9 said...

Thanks Zahid for the information.

When you say the TTI for LTE is 0.5sec. it arises a Q in my mind that when a resource can be shchedules min. in 1ms i.e. one sub frame or 2RB's then how can TTI be 0.5 sec. I may be wrong. Pls elaborate