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来源:LM317 Electronics Components编辑:enmo Technologies时间:2021-06-14 04:43:04

However, when the application demands more I/O such as in small machines or modular machine designs, an optional driveintegrated, IEC 61131-3-compliant PLC is an option. The PLC incorporates motion function block programming for profiling, electronic gearing, CAM profiles and other widely used motion control functions. Overall, the inclusion of a PLC in the drive reduces the number components for the overall machine control, but does not impact the machine builder's ability to leverage built-in safety technology.

There's a price to be paid for higher data rates. The typical constellation for 16-QAM has a smaller symbol decision area compared to QPSK. As a result, the received 16-QAM signal is more susceptible to spectral impairments, which translates into a tighter error vector magnitude (EVM) requirement for HSDPA receivers.

The EVM performance of the RF transceiver is adversely affected by four primary factors: phase and magnitude response of the receive filter; phase error due to the frequency synthesizer; I/Q mismatch; and dc offset (in direct conversion receivers).

MFR50SDBE52-89R8_Yageo

The application of programmable digital filtering in the transceiver can considerably improve the receiver's phase and magnitude response. Implementing digital equalization techniques in the transceiver can equalize the phase error. Digital calibration methods can also be applied to correct I/Q mismatch and dc offsets. Ensuring that the dynamic range of the analog-to-digital converters (ADCs) is optimized will also help mitigate EVM degradation. These digital-centric design enhancements are best implemented using nanometer CMOS technology, which provides the greatest integration, performance, and cost benefits.

Making such improvements to RF transceiver design is a must for better EVM performance. However, a more robust RF subsystem design is required to mitigate the effects of multi-path interference and fading conditions.

Receive diversity In high-density mobile environments, such as in cities and other urban areas, the mobile terminal is often subject to multi-path interference. In such cases, the received signal contains multiple noisy time-delayed copies of the desired signal (Fig. 2) . This type of interference can cause deep fading and even nulls at the receiver. Under such adverse radio conditions, data throughput and network efficiency can be greatly compromised.

MFR50SDBE52-89R8_Yageo

To reduce the degradation of signal integrity resulting from multi-path interference, receive diversity must be incorporated into the mobile device's RF subsystem. Diversity operation mitigates deep fades by enabling receivers to concurrently receive and process independent RF signals from two distinct antennas to maximize signal quality and reception. Receive diversity results in fewer fades in the combined signal, thus allowing the decoder in the baseband processor to perform better. The result is improved quality of service (QoS) throughout the entire cell and a boost in data rates of more than twice that of single-antenna designs.

MFR50SDBE52-89R8_Yageo

Receive diversity reduces basestation power requirements because less power needs to be transmitted to maintain a high-quality link between the basestation and the handset. With receive diversity, the mobile device can see” and process two signals instead of one, reducing the likelihood of the basestation having to transmit more power to contend with poor signal quality. This means that the cell coverage for existing subscribers can be extended and the saved system resources can be allocated to new subscribers. Simulation results demonstrate the advantage of receive diversity throughout the cell for both QPSK and 16-QAM in a Category 6 HSDPA network (Fig. 3) . At the middle of the cell, receive diversity improves throughput by more than twice that of non-diversity receivers.

To understand how a switch processes the frames that it receives and forwards, you will first learn about the three types of transmission methods found in a local-area network (LAN): unicast, multicast, and broadcast.

Transmission Methods LAN data transmissions at Layer 2 fall into three classifications: unicast, multicast, and broadcast. In each type of transmission, a single frame is sent to one node on the network. If the frame is to be sent to more than one node on the network, the sender must send individual unicast data streams to each node.

In a unicast transmission, a single frame or packet is sent from a single source to a single destination on a network. In a multicast transmission environment, a single data frame or a single source to multiple destinations packet is copied and sent to a specific subset of nodes on the network. In a broadcast transmission environment from a single source to all nodes, a single data frame or packet is copied and sent to all nodes on the network.

Unicast Unicast is a one-to-one transmission method in which the network carries a message to one receiver, such as from a server to a LAN workstation. In a unicast environment, even though multiple users might ask for the same information from the same server at the same time, such as a video clip, duplicate data streams are sent. One stream is sent to each user, as illustrated in the Figure 3.

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