Wireless Systems & Antennas

May 5, 2018 Off By sarvajeet

Wireless Systems & Antennas

Antenna technology analysis of LTE wireless systems Multiple input, multiple output ( MIMO) space Diversity antenna configuration specifically for 3GPP Long Term Evolution ( LTE) Designed for mobile communication systems. In fact, the LTE system specifies three types of antenna technologies: MIMO, Beamforming And diversity methods. How do these different antenna technologies work? Which kind of technology is the key to improving the robustness of signals and realizing the capabilities of LTE systems? Understanding these issues will help test systems that use these methods. This article will give the answerMulti-Input, Multiple-Output (MIMO) Space Diversity Antenna Configurations Specifically Designed for 3GPP Long Term Evolution (LTE) Mobile Communication Systems

meter. In fact, LTE systems specify three types of antenna technologies: MIMO, beamforming, and diversity methods. All three technologies are critical for improving signal robustness and achieving LTE system capabilities. Understanding how these different antenna technologies work, will help test systems that use these methods.

figure 1 provides a brief description of various antenna technologies. The name of each technology shows how the system’s transmitter and receiver access the wireless channel.A single input, single output (SISO) method with a single transmitter and a single receiver is the most basic wireless channel access mode.The multi-input, single-output (MISO) mode is slightly more complicated. It uses two or more transmit antennas and one receive antenna. In the MISO system (Often referred to as a transmit diversity system, the same data is sent to two transmit antennas, but the data is encoded so that the receiver can recognize which transmitter the data came from. Transmit diversity allows the signal to have stronger attenuation resistance and can improve performance under low signal-to-noise ratio (SNR) conditions. This technique does not directly increase the data rate, but it supports the existing rate with lower power consumption. The transmit diversity may be enhanced with feedback from the receiver indicating phase equalization and each antenna power. The single-input, multiple-output (SIMO) method (also commonly referred to as receive diversity technology) employs one transmit antenna and two or more receive antennas. Like the transmit diversity method, it is also well-suited to operate under low SNR conditions. Theoretically, 3 dB gain can be achieved when using two receivers. Because only one data stream is transmitted, the data rate is unchangedThe MIMO method requires two or more transmit antennas and two or more receive antennas. This mode is not simply a superimposition of MISO and SIMO since multiple data streams are transmitted at the same frequency and time, so the advantages of different paths within the wireless channel are fully utilized. The number of receivers in a MIMO system must be no less than the number of transmitted data streams. Please note that do not confuse the number of transmitted data streams with the number of transmit antennas. For example, in the case of transmit diversity (MISO), there are two transmit antennas but only one transmit stream. Superimposing SIMO on MISO will not result in a MIMO system, even if there are two transmit and receive antennas after superposition. Within the system, it is always possible that the number of transmitters is more than the number of data streams to be transmitted, but not vice versa. If N data streams are transmitted through less than N transmit antennas, the data will not be completely descrambled, no matter how many receivers. Overlapping data streams without spatial diversity can only create interference. However, if N data streams are distributed to N antennas at least in space, the interfering noise and noise in the wireless channel are low enough to cause no data loss, and N receivers can completely reconstruct the original data. data flowFor MIMO operation, the transmissions from each antenna must have unique identities so that each receiver can determine which combination of transmissions it receives. Identification is usually done with the aid of a pilot signal, which uses orthogonal modes for each antenna. In this case, spatial diversity to the wireless channel makes MIMO possible to increase the data rate. A basic form of MIMO is to allocate one data stream for each antenna (Figure 2). The channel then mixes the two transmissions so that, from the perspective of the receiver, each antenna receives a combination of individual data streams. Decoding of the received signal requires skill, where the receiver analyzes the pattern characterizing each transmitter to determine which combinations it represents. Using an inverse filter and accumulating the received data stream will reconstruct the original dataA more advanced form of MIMO includes special precoding to match the transmit and channel Eigen patterns. The optimization will distribute each pending data stream to more than one transmit antenna. In order to make the technology work efficiently, the transmitter must grasp the channel conditions and in some cases, these conditions must be fed back by the user equipment (UE) in real time. This optimization makes the system more complex but improves performance. The theoretical gain of a MIMO system is a function of the number of transmit and receive antennas, RF propagation conditions, the transmitter’s ability to adapt to changing conditions, and SNR. Ideally, the path within the wireless channel is irrelevant, as if it were an independent, physically-connected path and there is no interference between the transmitter and receiver. Since such a condition hardly exists in the real space, it is meaningless and impossible to refer to the MIMO gain without specifying the environmental conditions. The MIMO gain under ideal conditions is easier to determine. For a 2 × 2 system with two simultaneous data streams, double capacity and data rate are possible. MIMO technology performs best under high SNR and short sight distance conditions. The line-of-sight is equal to the channel cross interference. The longer the line-of-sight is, the less likely it is to increase the gain. Therefore, MIMO is particularly suitable for indoor environments that generally have multiple paths but limited line-of-sight.
Although the simple description in FIG. 1 does not specify whether multiple transmitters and receivers are used in a MIMO system, several sample details shown in FIG. 3 may be helpful in explaining different MIMO settings. The first case is a single-user MIMO (SU-MIMO) system, which is the most common form of MIMO and can be used for uplink or downlink of a wireless system. The basic goal of SU-MIMO is to increase the data rate for one user. Of course, it also increases the cell’s capacity accordingly. Figure 3 shows the downlink form of a 2×2 SU-MIMO system in which one user equipment is equipped with two data streams. In the example, the data stream is coded in red and blue; and in this case, it is further pre-coded in such a way that each stream is represented on each antenna with different power and phase. The color of the data stream changes at the transmitting antenna, which means that the data stream is mixed signaling. The transmitted signal is further mixed in the channel. The purpose of precoding is to optimize the transmission for the characteristics of the wireless channel so that when a signal is received it can be more easily segmented back into the original data streamTwo examples are 2×2 multi-user MIMO (MU-MIMO), which is only used for the uplink of the wireless system. (MU MIMO, as described in the WiMAX specification, is called cooperative spatial multiplexing or collaborative MIMO; however, LTE does not use this term). MU-MIMO does not increase the data rate of a single user, but it does provide a cellular capacity gain that is equal to or better than the gain that SU-MIMO can provide. In FIG. 3, these two data streams originate from different user devices. The two transmitters are farther apart than the single-user case, and the lack of a physical connection means that there is no opportunity to optimize the encoding to the Eigen mode of the channel by mixing two data streams. However, the extra spatial separation does indeed give the base station more opportunities—more specifically, the evolved Node B (eNB) elements in the radio access network—to “blind” user equipment with unassociated paths together. This maximizes the possible gain of capacity, which is different from the case of pre-coded SU MIMO where the antenna* will cause problems, especially at frequencies less than 1 GHz. MU MIMO has an additional important advantage: user equipment does not require the expense and power consumption of two transmitters, but cellular still benefits from increased capacity. In order to maximize the gain of MU MIMO, when the user equipment is installed in the base station, the time and power must be well organized

The third case in 3 is cooperative MIMO (Co-MIMO). Don’t mix this name with WiMAX’s collaborative MIMO. Co-MIMO involves two separate entities at the transmitting end. This example is a downlink scenario in which two eNBs “cooperate” to pre-code spatially separated antennas to achieve optimized communication with at least one of the user equipments. When this technique is used on the downlink, it is sometimes referred to as network MIMO. Downlink Co-MIMO has the best performance when the user equipment is on the edge of the cell. Here, the SNR will be the worst, but the wireless path will be irrelevant, which has great potential to improve performance.

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Graphical User Interface

Users can navigate the menu system of Dahua NVRs using the included USB mouse.

Dahua NVR Simple User Interface

The above screenshot shows the live camera view directly from the VGA and HDMI output of the Dahua NVR. The main menu seen on the bottom of the screen can be activated by clicking on the the mouse button with the mouse cursor near the bottom of the screen.