Comparing TD-SCDMA vs WCDMA : Frame and Physical Layer of td scdma

The meaning of TD-SCDMA 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. This tutorial delves into the frame structure and physical layer of TD-SCDMA, highlighting its unique characteristics and how it compares to WCDMA.

TD-SCDMA Frame Structure

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

The physical layer of TD-SCDMA is responsible for the actual transmission and reception of signals. It mainly consists of radio transceiver, modulation and demodulation, channel coding and decoding, synchronization, signal processing, multiplexing and demultiplexing etc.

The figure depicts detailed block diagram of TD SCDMA physical layer modules. Refer transmitter part of UTRA Physical Layer defined in 3GPP standard for TDD mode.

Difference between td-scdma and wcdma

Let us compare TD-SCDMA vs WCDMA and derives differences between these technologies.

References

TD-SCDMA Forum, Website- www.tdscdma-forum.org/en/

Summary

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 TD SCDMA.

These technologies offer distinct approaches to mobile communication, with TD-SCDMA utilizing a combination of time and code division techniques and WCDMA employing pure code division methods. Understanding their frame structures and physical layer components provides a clear picture of how these technologies manage spectrum and data transmission.

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