Future mobile communication systems demand much higher data rates which may require significantly more energy consumption, compared with the current 3G systems. Recently, green radio has attracted worldwide attention. Energy efficiency is considered as a very important factor for designing future communication systems in this green radio environment because reducing energy consumption of base stations (BSs) and mobile stations (MSs) can directly contribute to reducing CO ₂ emission. We investigate the effects of cell size on energy saving and system capacity and then show the effectiveness of small-cell based future mobile communication systems in terms of energy efficiency. If the path-loss exponent increases and cell-radius ratio becomes smaller, the per-energy capacity ratio becomes larger. For example, if the path-loss exponent is 4 and the per-energy capacity of a macro-cell is normalized to 1, the per-energy capacities of a micro, pico-, and femto-cell are 16,10 ⁴ , and 10 ⁸ in downlink and 64,10 ⁶ , and 10 ¹² in uplink, respectively. The amount of CO ₂ emission of one BS transmitter is approximately 181[kg] in a year, if the cell radius is 1[km]. If the cell radius is 500[m], 100[m], and 10[m], the amount of CO ₂ emission in a year is reduced to 45.25[kg], 1.81[kg], and 18.1[g], respectively. Thus, small-cell based mobile communication systems can be a very effective solution to accommodate high data rates with low energy consumption in a future green radio environment.

Seon Yeob Baek

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