Regardless of how the broader market fluctuates, a bond's coupon remains consistent (unless the bond is inflation-protected). The coupon is the dollar value of the payments you receive. As the bond market fluctuates, the price of your bond may rise or fall. If it rises, then the yield rate will decrease, because the coupon doesn't increase in step with the bond price. This doesn't significantly impact bondholders who plan on buying and holding bonds until maturity.