What is tdscdma ?
The meaning of TDSCDMA is Time Division Synchronous Code Division Multiple Access. It is also referred as china's 3G standard similar to Europe's 3G (WCDMA). TD-SCDMA uses various frequency bands from 1785MHz to 2220 MHz range. It uses bandwidth of either 1.6MHz or 5 MHz based on Mcps requirement.
As shown in the figure 1, TD-SCDMA uses single unpaired spectrum for both downlink (DL) and uplink (UL) traffic. TDD is employed to provide access to both uplink and downlink traffic in different time slots on this shared spectrum. TD-SCDMA uses spectrum efficiently by allocating time slots as per data load requirement in downlink and uplink and hence it is ideal for asymmetric traffic.
TD-SCDMA frame structure is shown in figure 2, which depicts frame hierarchy. In TD-SCDMA a super-frame of 720 ms duration is made of 72 radio frames of 10 ms duration each. Further each radio frame is divided into two sub frames each of 5ms. One sub frame is composed of 7 normal time slots used for downlink/uplink and 3 special time slots. In 7 normal time slots, slot TS0 is used for downlink, slot TS1 for uplink and rest of time slots are allocated based on demand for traffic in downlink/uplink. 3 special time slots are used as DwPTS (downlink pilot timeslot), GP (guard period) and UpPTS (uplink pilot timeslot). DwPTS and UpPTS are used for downlink and uplink synchronization respectively. For 1.28 Mcps TDD case, 1.6 MHz is allocated and for 3.84Mcps TDD case 5 MHZ is allocated. Information data bits are spread across using CDMA codes. 16 codes are allocated for each time slot.
TD-SCDMA Physical layer
Follow link below to read more on TD-SCDMA Physical layer modules used in transmitter part as per UTRA Physical Layer defined in 3GPP standard for TDD mode.
Difference between td-scdma vs wcdma
Let us compare TD-SCDMA vs WCDMA and derives difference between TD-SCDMA and WCDMA technologies in table format below.
|Duplex scheme||TDD (Time Division Duplex)||FDD (Frequency Division Duplex)|
|Frequency bands||Shared frequency band for uplink/downlink||Separate frequency bands for uplink/downlink|
|Interference susceptibility||More susceptible to interference due to TDD||Less susceptible to interference due to FDD|
|Global adoption||Limited, primarily used in China||Widely adopted worldwide as UMTS|
|Spectral efficiency||1.25 bit/sec/Hz||1 bit/sec/Hz|
|Capacity||2.5 Mbps/cell||2 Mbps/cell|
|Data focus||Designed with a focus on data services||Supports both voice and data services|
|Evolution and standards||Limited evolution||Evolved into HSPA, HSPA+ and beyond|
TD-SCDMA Forum, Website- www.tdscdma-forum.org/en/
Conclusion : TD-SCDMA had limited adoption outside of China. It was primarily used in Chinese 3G telecom networks. As the mobile technology continued to evolve from 4G LTE to 5G NR and 6G, these cellular technologies will overshadow presence of TDSCDMA.
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