Mobile TV is considered to be one of the most promising multimedia services in the 3G era. It combines multimedia, real-time, interactive and many other media features. The terminal is lightweight and mobile, and users can easily access services. MBMS (MulTImedia Broadcast MulTIcast Service) is a multimedia broadcast multicast function defined by 3GPP R6, which can provide mobile TV services in mobile communication systems.

The main changes caused by MBMS are: adding BM-SC network elements; upgrading existing network elements of the packet domain to support MBMS-specific interface functions (such as Gmb), unique channels (such as MICH, MTCH / MCCH / MSCH), Unique physical layer processes (FACH channel selective combining, PTM and PTP switching) and unique business processes (such as subscriptions). A single frequency network (SFN) is introduced at the physical layer, and several base stations simultaneously transmit the same signal on the same frequency. The spectrum efficiency is improved, and the UE (user equipment) does not need any handover when moving within the SFN, which greatly reduces the signaling overhead.

TD-MBMS is a mobile TV standard for TD-SCDMA and has been adopted at CCSA and 3GPP. TD-MBMS is based on 3GPP MBMS and is based on SFN, further introducing UTN (Union TIme-slot Network) technology.

1 Introduction to TD-MBMS

See Figure 1. In an SFN environment, signals from different base stations can be equivalent to multipath signals. The receiver does not need to distinguish whether the signals are from different base stations, and the complexity is greatly reduced. In the original base station, there is co-channel interference, and the mobile phone needs to perform complex calculation to eliminate interference. However, in the SFN, because the multipath signal is rich, the receiving performance is greatly improved, thereby improving the spectrum utilization.

TD-SCDMA is a time division duplex (TDD) system, and the uplink and downlink occupy the same frequency. In TD-SCDMA, the single frequency network with separate frequency points is not suitable, and it faces the problem of spectrum resources; it may cause strong interference between the time slot (downlink) of the MBMS frequency point and the same time slot (upstream) of the non-MBMS frequency point. Individual frequency points are also not conducive to resource planning and sharing receivers with N-frequency systems. Therefore, a simultaneous slot network (UTN) is introduced in TD-MBMS.

SFN

Figure 1 Schematic diagram of SFN (single frequency network)

Figure 2 shows a schematic diagram of the joint network of N-frequency and UTN. The downlink time slot may be configured as a UTN or N frequency point time slot; the UTN occupied time slots may be the same or different between different frequency points in the cell; but the UTN time slot allocation of the same frequency point of the adjacent cells is the same. The UTN time slot is used to transmit an MBMS broadcast service, in which a plurality of base stations participating in the broadcast transmit the same signal. In fact, the UTN time slot can be viewed as a separate SFN wireless network that is time division multiplexed with the N-frequency network. [1]

N frequency point in TD-MBMS

Figure 2 N-frequency + UTN networking in TD-MBMS

The UTN time slot uses a common Midamble code and a scrambling code, that is, the parameters of the local cell and the neighboring cell are the same; between the neighboring cells, the data transmitted by the time slot is also formed by the same processing of the same data. For other N-frequency slots, the cell-specific Midamble code and scrambling code are used. TS6 (time slot 6) is usually not used as a UTN time slot. Otherwise, when the mobile phone receives the MBMS service at the secondary frequency point, there may not be enough time to switch to the TS0 of the primary frequency point due to the limitation of the radio frequency device.

The UTN frequency and time slot resources of the N-frequency system can be flexibly configured, for example, more downlink time slots are allocated to the UTN; the number of UTN time slots at each frequency point is different to accommodate services of different rates.

2 The impact of delay spread on performance

The UTN network has increased the requirements for multipath delays tolerated by mobile phone receivers, which was studied in reference [2]. The simulation shows that in the case of SFN, the receiver window width of the receiver has a significant impact on the reception performance. The larger the receiving window width, the larger the received signal to interference ratio. In the case of the same receiver window width, the smaller the cell radius, the larger the proportion of the cell area occupied by the area where the signal to interference ratio is greater than the given threshold.

The frame structure and receiver of the TD-SCMDA are designed for delay spread of 16 chips. Referring to reference [3], the simulation further shows that a 16-chip (12.5 microsecond) receive window can tolerate multipath delay spread in an SFN environment. Especially in the urban area, the cell radius is small, the base station density is large, and the obstacles are dense, which greatly reduces the delayed signal energy falling outside the 16 chips.

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4. Voltage: DC12V
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6. Luminous flux: 270-300LM
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9. Warranty: One year (under normal use)

SMD335 Led Strip Light SMD335 Led Strip Light
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SMD335 Led Strip Light

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SMD335 Led Strip Light

SMD335 Led Strip Light

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