OFDMA Principles in LTE
Orthogonal Frequency Division Multiple Access (OFDMA) is a key technology used in Long-Term Evolution (LTE) to efficiently manage the transmission of data over the radio interface. Here’s an explanation of OFDMA principles in LTE:
- Frequency Division Multiplexing (FDM): OFDMA uses FDM to divide the available frequency spectrum into multiple subcarriers. Each subcarrier is then assigned to individual users or used for specific purposes.
- Orthogonality: The term “Orthogonal” in OFDMA implies that the subcarriers are orthogonal to each other, meaning there is no interference between them. This orthogonality is achieved through precise timing and frequency synchronization.
- Subcarrier Spacing: In LTE, the subcarriers are spaced at regular intervals. The standard specifies different subcarrier spacings (e.g., 15 kHz, 30 kHz) depending on the LTE deployment scenario.
- Resource Blocks (RBs): The LTE spectrum is divided into resource blocks, and each resource block consists of a certain number of subcarriers in the frequency domain and a certain number of symbols in the time domain. Resource Blocks are the basic unit for resource allocation in LTE.
- Dynamic Resource Allocation: OFDMA allows for dynamic resource allocation, meaning that resources (subcarriers) can be assigned to users based on their instantaneous demand and channel conditions. This flexibility improves the efficiency of resource utilization.
- Adaptive Modulation and Coding (AMC): OFDMA enables adaptive modulation and coding, allowing different users to use different modulation schemes and coding rates based on their channel conditions. Users in good radio conditions can use higher-order modulations for increased data rates.
- Support for Multiple Users: OFDMA enables the simultaneous transmission of data to multiple users in the same time and frequency resources. This is achieved by assigning different subcarriers to different users, allowing for multiple access.
- Improved Performance in Frequency-Selective Channels: OFDMA is well-suited for dealing with frequency-selective fading, where different frequency components of the signal experience different levels of fading. The use of orthogonal subcarriers helps mitigate the effects of frequency-selective fading.
In summary, OFDMA in LTE utilizes the principles of frequency division, orthogonality, and dynamic resource allocation to efficiently manage and transmit data over the wireless channel, providing a flexible and adaptive approach to meet the diverse communication needs in LTE networks.
There are several ways to transmit over the frequency band and to share the resource between several devices. What is TDMA,CDMA & FDMA ?
• The users are separated by the the time
• Used by the GSM
• The users are separated by the codes. They receive data at the same time at the same frequency.
• Used in the CDMAOne, CDMA2000 and WCDMA
• The users are separated by the frequency
• The 3G LTE used an improved FDMA called OFDMA