Announcement this week that the Chinese government is backing the use of 2.6GHz band for TD-LTE by allocating spectrum for this, a big deal for Clearwire because this will very likely lead to economies of scale that will bring equipment cost down – but not sure what good that will do if main equipment vendor is ZTE or Huawei given the Congressional committee’s scathing comments last week.
Huawei Technologies Co. Ltd. and ZTE Corp., China’s two biggest makers of telecommunications equipment, are facing intense scrutiny thanks to a US House Intelligence Committee report, the result of an 11-month fact-finding mission. The crux of the recommendation is the two companies’ failure to provide documents that detail their relationships, and regulatory interaction with Chinese authorities. Presumably, the fear is that Huawei and ZTE could somehow build backdoors into their routers and switches, leaking sensitive information to the Chinese government.
Advantages of LTE TDD vs FDD include:
  • Lower hardware cost because diplexer not needed. Needed in LTE-FDD because of use of paired spectrum.
  • Channel propagation is the same in the uplink and downlink path because of use of the same frequency making channel tuning easier.
  • Possible to dynamically change the UL and DL capacity ratio to match demand (by assigning different width time slots).
  • Advantage to China is that this is a natural upgrade path from TD-SCDMA which also uses unpaired spectrum.

Disadvantages:
  • Unlike in LTE-FDD where guardband already provided to ensure isolation between UL and DL, in LTE-TD need to provide this guard interval and a larger guard interval required if distances are increased (because of longer propagation times) which could affect capacity.
  • Discontinuous transmission which can degrade the performance of the RF power amplifier in the transmitter.
  • eNodeB’s need to be synch’d with respect to the UL and LD transmission time slots to avoid cross-slot interference. If other eNodeB’s use different UL and DL assignments, and share the same CH, then interference may occur between cells.