Lte University Expert Quiz - 2009

OFDMA systems use orthogonal subcarriers, which means that each subcarrier is orthogonal to the others. This orthogonality allows adjacent subcarriers to be used without interference because they do not overlap in the frequency domain. As a result, multiple users can transmit simultaneously on different subcarriers without causing interference to each other.

The largest channel bandwidth a UE is required to support in LTE is 20 MHz. This means that the UE must be able to handle a bandwidth of up to 20 MHz for data transmission and reception. This allows for faster data speeds and increased capacity on the LTE network.

3GPP, or the 3rd Generation Partnership Project, is the organization responsible for developing LTE (Long-Term Evolution) standards. LTE is a wireless communication technology that provides high-speed data transmission and is commonly used in 4G networks. UMTS (Universal Mobile Telecommunications System) is a 3G technology, 3GPP2 is a different organization responsible for CDMA2000 standards, and ISO (International Organization for Standardization) is a non-governmental organization that develops various international standards but not specifically related to LTE.

The number of transmit antennas in MIMO (Multiple-Input Multiple-Output) systems has the greatest influence on data rates. MIMO technology utilizes multiple antennas for both transmission and reception, allowing for the simultaneous transmission of multiple data streams. By increasing the number of transmit antennas, more data streams can be transmitted simultaneously, resulting in higher data rates. Therefore, the number of transmit antennas is the factor that has the greatest impact on data rates in MIMO systems.

The DC subcarrier indicates the center of the OFDM channel. In OFDM (Orthogonal Frequency Division Multiplexing), the channel is divided into multiple subcarriers. The DC subcarrier represents the zero frequency, which is located at the center of the channel. It helps in maintaining the orthogonality between the subcarriers and is used as a reference point for the other subcarriers.

The correct answer is hard handover only. In LTE, only hard handovers are supported. Hard handover refers to the process of transferring a call or data session from one cell to another, where the connection is briefly interrupted during the handover. Soft handover, on the other hand, allows for seamless handovers between multiple cells, where the connection is maintained with multiple cells simultaneously. Softer handover is not a supported handover type in LTE.

The correct answer is IFFT. IFFT stands for Inverse Fast Fourier Transform, which is a processing step that combines multiple OFDM (Orthogonal Frequency Division Multiplexing) subcarriers into a single signal for transmission. OFDM is a modulation technique that divides the available spectrum into multiple subcarriers, and IFFT is used to convert these subcarriers back into the time domain, resulting in a single signal that can be transmitted over the channel.

A Cyclic Prefix (CP) is required in OFDMA (Orthogonal Frequency Division Multiple Access) to prevent inter-symbol interference (ISI) and maintain orthogonality between subcarriers in a multi-path environment. It does this by copying the end portion of the OFDM symbol and adding it to the beginning, allowing time for echoes to settle before the next symbol starts. This improves data integrity in wireless communication systems.

The PCFICH (Physical Control Format Indicator Channel) is the channel that indicates the number of symbols used by the PDCCH (Physical Downlink Control Channel). The PCFICH is used to inform the UE (User Equipment) about the number of OFDM (Orthogonal Frequency Division Multiplexing) symbols used for the PDCCH in each subframe. This information is necessary for the UE to correctly decode the PDCCH and extract control information. Therefore, the PCFICH is the channel that provides the indication of the number of symbols used by the PDCCH.

The benefit of PAPR reduction in the uplink in LTE is that it leads to improved uplink coverage, lower UE power consumption, and reduced equalizer complexity. By reducing the peak-to-average power ratio (PAPR), the uplink signals become more efficient and less susceptible to interference, resulting in improved coverage. Additionally, lower PAPR reduces the power requirements for the user equipment (UE), leading to lower power consumption. Furthermore, reduced PAPR simplifies the equalization process, making it less complex and more efficient. Therefore, all of the given options - improved uplink coverage, lower UE power consumption, and reduced equalizer complexity - are benefits of PAPR reduction in the uplink in LTE.

The suitable cell provides the best level of service for average subscribers. This implies that it meets the requirements and expectations of the majority of subscribers, offering them a satisfactory level of service. The other options, such as the acceptable cell, barred cell, and reserved cell, may not provide the same level of service or may have certain limitations or restrictions that make them less suitable for average subscribers.

The PBCH (Physical Broadcast Channel) is scrambled with the physical cell ID. Scrambling is a process used in wireless communication to add a pseudo-random sequence to the transmitted signal, which helps differentiate it from other signals and reduce interference. The physical cell ID is a unique identifier assigned to each cell in a cellular network, and it is used for various purposes, including cell identification and synchronization. Scrambling the PBCH with the physical cell ID ensures that the PBCH signal can be correctly received and decoded by the receiving devices within the cell.

The length of the shortest possible PDCCH is 72 bits.

Transparent Mode (TM) adds the least amount of delay to user traffic compared to the other RLC modes. In Transparent Mode, the RLC layer does not introduce any additional delay for retransmissions or acknowledgments. It simply passes the user data from the upper layers to the lower layers without any processing or error checking. This mode is suitable for applications that require low latency and real-time communication, as it minimizes the delay in delivering user traffic.

The Cyclic Prefix is a copy of the tail end of the symbol in order to ensure a continuous time domain signal. This is important because it helps in reducing the effects of inter-symbol interference (ISI) caused by multipath propagation. By adding the cyclic prefix, the receiver can effectively remove the ISI and recover the original symbol without any distortion. This is achieved by using the cyclic prefix to eliminate the interference from the previous symbol and maintain a continuous signal in the time domain.

The physical cell ID cannot be determined from the synchronization signals because the primary synchronization sequence (x) and the secondary synchronization sequence (y) do not provide enough information to determine the physical cell ID. Therefore, the physical cell ID is represented by x+3y.

In a communication system that uses the normal Cyclic Prefix, each symbol is preceded by a cyclic prefix that helps in reducing inter-symbol interference. The length of the cyclic prefix is typically a fraction of the symbol duration. Since the cyclic prefix is added to each symbol, the total number of symbols in 1 frame will be the same as the number of symbols without the cyclic prefix. Therefore, the correct answer is 140.

The primary and secondary synchronization signals in a communication system require a bandwidth of 1.08 MHz to be transmitted.

Approximately half of a subframe in a 1.4 MHz channel is available for carrying the Physical Downlink Shared Channel (PDSCH).

The odds of two UE's colliding during their random accesses can be determined by calculating the probability of collision. In PRACH configuration 14, there are a total of 64 preambles available for random access. Each UE randomly selects one of these preambles. The probability of two UE's selecting the same preamble is 1/64. Therefore, the odds of collision occurring is 1 in 64. However, the question asks for the odds of collision, so we need to calculate the probability of no collision. The probability of no collision is 1 - (1/64), which is approximately 0.984. Therefore, the odds of two UE's colliding during their random accesses is 1 in 1/0.984, which is approximately 1 in 640.