Jump to content

Hong Kong's CSL demos 300Mbps LTE Advanced service, due early 2014 (video


Recommended Posts

probably 4x4 mimo

It's actually 2x2 MIMO aggregating two 2x20Mhz FDD component carriers. One in Band 3 and other in Band 7. This will require Category 6 User Equipment which is due next year by the way of Qualcomm and Intel.


Notice how all the baseband chipset vendors decided to skip Cat 5 which mandated 4x4 MIMO. From a business standpoint looks like that isn't happening simply because it's a bitch to cramp 4x4 into small form factor without some breakthrough interference coordination, which doesn't exist. Also, that'd absolutely eat batteries for breakfast. 


So they all are opting to go with "more aggregated spectrum" and 2x2 MIMO route for the time being.

Link to comment
Share on other sites

Isn't Sprint using a 20Mhz TD-LTE carrier? How is it that Sprint gets up to 90 Mbps and this carrier gets 150 off of a single carrier of the same size? Unless Sprint is using a 10Mhz TD-LTE carrier.

For a 2x2 MIMO LTE airlink

Downlink Peak speed = 7.5 Mbps/Hz * Downlink bandwidth


So for a 20mhz FDD link you have 20mhz downlink spectrum and 20mHz uplink or 20+20 MHz = 40mHz of total spectrum


For download speeds we only care about the downlink bandwidth (20mHz in this case)




peak download speed = 20mHz * 7.5mbps/MHz = 150mbps


For TDD air links a single chunk of spectrum is used for upload and download. The connection is separated by time division. There is a time allocated to upload and a time to download. This doesn't have to be symmetric either. In Sprint's case they have a 3:2 download to upload ratio which means that 3/5 = 60% of the time the airlink is in a downlink state for your device.


To calculate the peak downlink speed of a TDD air link take the ratio (3 downlink to 2 uplink) add the two factors together to get 5. Next divide the downlink by the total time ( 3 / 5 = 0.60 = 60%). This is your downlink percentage that I described earlier.


Now take your TDD bandwidth (for Sprint 20mHZ) multiply it by your percentage and you get you downlink bandwidth (0.6 * 20mHz = 12 MHz). Finally multiply your downlink bandwidth by the standard LTE peak spectral efficiency of 7.5mbps/MHz




Max DL Speed = 20mHz TDD bandwidth * (0.60 DL percentage) * 7.5 Mbps/MHz = 90mbps


For carrier aggregation multiply your airlink speeds by the number of channels. So for 2 aggregated 20mHz TDD channels the max speed is


2 channels * 90mbps/channel = 180mbps


Or for 20mHz FDD


2 channels * 150mbps/channel = 300mbps

  • Like 4
Link to comment
Share on other sites


Sprint is TDD and that carrier is FDD. Even though they sound similar (20mHz FDD and 20mHz TDD), the reality is that the FDD carrier actually is using twice the spectrum but TDD makes up for it partially by being able to allocate more of its spectrum to uploading.

20mHz FDD

20mHz Downlink spectrum
20mHz Uplink Spectrum

20mHz TDD

20mhz Downlink/Uplink

For Sprint's 3:2 DL to UL ratio

12mHz Downlink
8mHz Uplink

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...