Emerging 5G URLLC wireless systems are characterized by minimal over-the-air latency and stringent decoding error requirements. The low latency requirements can cause conflicts with 5G EE design targets. Therefore, this work provides a perspective on various trade-offs between energy efficiency and user plane delay for upcoming URLLC systems. For network infrastructure EE, we propose solutions that optimize base station on-off switching and distributed access network architectures. For URLLC devices, we advocate solutions that optimize EE of discontinuous reception
(DRX), mobility measurements, and the handover process, respectively, without compromising on delay.
1. URLLC requirements cannot be met with existing 4G access technologies such as Release 14 LTE, since the minimum transmission time interval (TTI) is 1 ms1 and the typical data packet error rate target is 10–1. Furthermore, uplink (UL) LTE transmissions generally follow a three-step sequence of:
• Scheduling request on UL
• UL grant from eNB
• UL transmission after several TTIs
2. The NR air interface is based on cyclic prefix- orthogonal frequency-division multiplexing (CP-OFDM) as in LTE. However, multiple OFDM subcarrier spacing are supported ([15, 30, 60, 120, 240] kHz) as opposed to the 15 kHz used for LTE data and control channels.
3. Furthermore, a TTI in NR can be as short as two OFDM symbols; a two-symbol transmission with 120 kHz subcarrier spacing would span (1/(120 × 103)) = 16.67 ms in the time domain (excluding CP).
4. A key feature in 5G NR is the utilization of large-scale antenna arrays, or so-called massive multiple-input multiple-output (MIMO) for advanced beam forming.
5. The continuous, Omni directional transmission of wideband cell-specific reference signals (CRSs) every DL sub frame in LTE is wasteful if there are no or few UEs attached to the cell.
1. LTE was originally designed to have always-on DL transmissions from the eNB; specifically, certain wideband reference signals are transmitted every TTI. This leads to poor EE when there are no active UEs or no DL traffic to serve.
2. The concept of evolved Node B (eNB) on-off switching was introduced in Release-12 as a remedy, where eNBs could suspend all transmissions for tens of milliseconds, without the need for handover of the served UEs to another eNB.
3. The EE-delay trade-off is apparent when extending this concept to gNB on-off switching for URLLC: going into off mode can conserve energy, but leads to delays in delivering and receiving URLLC traffic.
Reliability is ensured by using very low-rate error correction coding together with multi- antenna beam forming.
2. Energy Efficiency:
We have seen so far that URLLC has stringent delay and reliability requirements. Energy efficiency has not been assigned explicitly as a performance metric for URLLC.
Reception delay or latency in 4G and 5G systems can be divided into two major parts: user plane (UP) latency and control plane (C-Plane) latency
HARDWARE AND SOFTWARE REQUIREMENT:
Operating System : Linux
Simulation Tool : NS2
CPU type : Intel Pentium 4
Clock speed : 3.0 GHz
Ram size : 512 MB
Hard disk capacity : 80 GB
Monitor type : 15 Inch color monitor
Keyboard type : Internet keyboard
CD -drive type : 52xmax
T. Camp, J. Boleng, and V. Davies, ``A survey of mobility models for ad hoc network research, Wireless Commun. Mobile Comput., vol. 2, no. 5, pp. 483_502, 2002.